Borderline personality disorder (BPD) is characterized by difficulties in regulating emotions, lack of impulse control, self-identity problems, and chaotic relationship patterns, along with frantic efforts to avoid abandonment [1]. Individuals with BPD struggle to effectively cope with their negative thoughts and emotions such as anger, emptiness, and fear, leading to various dysfunctional behaviors, including deliberately selfinjurious and other impulsive actions [2]. Consequently, even among health professionals, BPD is considered a severe psychiatric health problem, often evoking uneasiness and feelings of being manipulated and challenged [3].

Moreover, significant others of individuals with BPD are also associated with increased rates of mental health problems, experiencing high levels of psychological distress, as they are exposed to the patients’ dysfunctional behaviors [4]. In an interview study, the strain of being the significant other of someone with BPD was so immense that they described their life as a “tiptoeing,” mostly because of a 24-hour sense of duty and constant worry [5]. Additionally, their identity disturbance and low self-worth make them more vulnerable than other psychiatric patients; thus, individuals with BPD are likely to require constant understanding and validation to endure and relieve suffering [6].

Interpersonal hypersensitivity is a central feature of BPD. The relationship patterns of individuals with BPD were intense but unstable, shifting between two extremes of idealization and devaluation and involving both needs for intimacy and fears of rejection [7]. Interpersonal aggression, in those with BPD, particularly in response to social rejection cues, likely results in an increased probability of problematic relationships by disrupting interpersonal functioning [8].

Based on the attachment theory, rejection sensitivity (RS) is defined as a cognitive-affective process in which individuals anxiously expect and are ready to perceive intentional rejection, thus overreacting to the perceived rejection [9,10]. When individuals with heightened RS, who tend to be hypervigilant for rejection signs, perceive potential rejection, they are more likely to respond with hostility, aggressive behaviors, and attempt to control someone else [11]. The risk of developing fears and expectations of rejection is increased by early traumatic experiences in abusive and rejecting family environments [12]. Therefore, BPD patients, frequently experiencing maladaptive childhood and invalidating family environments [13], are predicted to be highly sensitive to rejection [14-16]. Although individuals with BPD would like to be more accepted, develop trust toward others, and end their unstable relationships [17], the perception of rejection triggers their behaviors characterized as clinging or withdrawal, aggressive and risky, or dismissive [18].

According to the shared experiences posted online by individuals with BPD, they commonly talk about their favorite person (FP) and how having an FP negatively impacts and worsens their BPD symptoms. FP is someone who individuals with BPD often hold in the highest regard trust with their life, and are heavily emotionally attached to and dependent on [19]. They often unintentionally put their entire self-worth into the relationship with their FP, thereby making frantic efforts to prevent their FP from leaving. An FP, therefore, is likely to receive the brunt of all the intensity and instability arising from being in an intimate relationship with someone with BPD. As having an FP is a challenge for someone with BPD, developing a better understanding of the relationship pattern and its potential profound impact on them would make it possible to explore effective ways of keeping the relationship healthier.

Although research into interpersonal dysfunction, characteristic of BPD, has been accumulated to develop a comprehensive understanding of BPD’s interpersonal context and impact on relationship quality and mental health, gaps in the research remain to be addressed. The relationship between individuals with BPD and their FP, to the authors’ knowledge, has rarely been explored. Despite an increasing number of studies that investigate the dysfunctional relationships of individuals with BPD, no studies have explicitly attempted to differentiate this mutually destructive FP-BPD relationship by examining actual experiences of those with BPD. To investigate the FP-BPD relationship’s phenomenological experience and capture the FP characteristics based on how they are described by their person with BPD, an in-depth review of actual experiences explained by individuals with BPD is required.

To address the research gaps, this study aims to identify common experiences of individuals with BPD and review the experiential support for the dysfunctional FP-BPD relationship pattern described by them. Furthermore, this study aims to investigate the role of FP in this relationship and how they affect the emotions and actions of their person with BPD. Building on this FP-BPD relationship pattern, we argue that a particular type of person should be more likely to become an FP and get involved in this unhealthy relationship.

Figure 1 demonstrates a visual representation of word frequency derived from 207 public posts and comments regarding the FP-BPD relationship. The more often the word appeared within written texts being analyzed, the larger it appeared in the generated figure. Despite giving a synopsis of significant keywords regarding the FP relationship concept and identifying the focus of collected data, it fails to classify and group words implying a similar or same meaning, for example, ‘feel’ and ‘felt’ or ‘depend’ and ‘reli.’

Thus, we reorganized and categorized the frequently-appeared keywords into five groups according to their apparent meanings to enhance our understanding (Table 1). Category 1 includes words related to the development of FP attachment, implying what makes those with BPD likely to form an intense attachment to a particular person. Words in category 2 refer to relationship characteristics; writers frequently used them to describe the FP relationship characteristics. Category 3, named emotional and cognitive responses, indicates how those with BPD feel or think about their FP relationship. Category 4 refers to the relationship types, such as friend and partner. Category 5 includes relationship-associated words often used to explain how their FP relationship begins and breaks down regardless of their intention. Furthermore, we qualitatively reviewed and put collected data together following the common FP relationship pattern.

Overall, our findings indicate that those with BPD tend to form an intense and insecure attachment towards their FP. Individuals with BPD experience intimate and unstable relationship struggles while alternating between extremes of idealization and devaluation and making desperate efforts not to be abandoned [35,36]. This study reveals that struggles, such as fear of abandonment, constant splitting, and overwhelming feelings, experienced in FP relationship are even more intense and devastating. As their FP-love goes beyond their control, making them increasingly obsessed with their FP, the relationship often gets to the point where their desperate attempts to keep their FP in their life eventually drive them away. FP relationship seems likely to become unhealthy and destructive, sustaining and intensifying the expression of BPD individual’s symptoms. Consistently, research has found that BPD symptoms including hypersensitivity to rejection tend to emerge and get worse in close relationships with their attachment figures [8,37].

Although BPD symptoms influence FP relationship quality, we suggest that the personality of the FPs whom those with BPD strongly attach to has a significant effect throughout their relationship. The personality of the partners whom those with BPD choose partially but significantly affects BPD symptom intensity and the relationships’ success [38,39]. FPs’ personality factors are essential to understand. Our study reveals that FPs seem exceptional enough for those with BPD to form a strong obsession and undefined, intense feelings toward them. They also appear highly tolerant until the situation becomes unbearable, especially when they are not their family or involved romantically or sexually with their person with BPD.

The destructive FP relationship pattern implies that most FPs share particular characteristics that make them more likely to become an FP and contribute to the formation of toxic FP attachment. Identifying the shared personality traits in many, if not all, FPs to understand the relationship from which those with BPD enormously suffer is crucial. Our findings reveal that certain FPs gradually intensify their person with BPD’s symptoms and assume avoidance behaviors when conflicts arise. In this study, for convenience, we address them distinctively as “Teddy Bear Person (or TBP),” based on previous research, demonstrating that patients with BPD tend to develop a problematic attachment to and emotionally rely on transitional objects, such as stuffed animals, that would provide them with emotional comfort and stability [40-42]. The association between transitional object attachment and BPD was so strong that carrying stuffed animals to hospital settings was also referred to as the “positive bear sign.” [43]

Considering the BPD traits and TBPs’ observed behaviors, we suggest that their destructive relationship may be explained based on the RS model. BPD individuals with high RS have difficulties controlling their intense anger and a greater tendency to display hostile and aggressive behaviors in response to rejection threats [19,36]. However, TBPs, who we suggest contribute to an unhealthy FP relationship development, exhibit ambivalent behaviors in response to their person with BPD’s symptoms; they are understanding and caring, but sometimes appear detached, provoking greater confusion and BPD splitting. Because the intimidating way BPD individuals respond to social interaction can be another interpersonal threat to others, particularly hypersensitive individuals, we argue that TBPs more vulnerable to borderline personality traits (e.g., anger, impulsivity, or splitting) would also be likely to have heightened RS, similar to those with BPD.

The RS model explains that those who expect rejection angrily tend to express aggression and use coercion in response, while others who expect rejection anxiously tend to avoid conflicts by self-silencing and compliance or social withdrawal [44,45]. Angry RS is more strongly associated with reactive hostility and anger; thus, individuals with high angry RS are more likely to respond with aggressive retribution, often provoking interpersonal conflict [46,47]. Individuals with higher anxious RS, however, are more likely to prevent rejection before it occurs. They make efforts not to lose their relationship primarily by inhibiting their feelings and actions that might upset the other person or being more solicitous and obliging to please them [48]. Moreover, they have a greater tendency to avoid or withdraw from relationships once conflicts arise and hardly see the possibility of acceptance [49,50].

Considering that the form of-angry or anxious-RS they present may predispose high RS individuals to respond differently to interpersonal conflicts [51], we contend that this difference may partially explain the interaction between TBP and their person with BPD and their behavioral changes throughout the relationship. We suggest that TBPs’ high RS may interact synergistically with that of their person with BPD to strengthen their reactive responses and BPD symptoms, thereby developing a mutually destructive relationship. However, more research is needed to conceptualize the FP relationship; further attempts are required to address the dysfunctional interaction based on the RS model and differentiate TBPs, among FPs, from non-TBPs.

In sum, this study addresses that those with BPD tend to form a particular type of intense and unstable attachment to so-called ‘FP,’ who can include their friends, romantic partners, or family members, though most likely their friends. Notably, this FP relationship is often dysfunctional, but BPD characteristics may not fully explain the relationship’s intensity and instability because they do not develop FP attachment toward all the individuals close to them, even if they are romantically or sexually involved. Therefore, we assert that many FPs (distinctively named as TBP in this study), but not all, may be predisposed to behave in a particular manner. Their personality factors (e.g., RS) may interact with the other person’s BPD characteristics and increase the likelihood of the FP relationship becoming unhealthy and maladaptive.

However, this study’s limitations could be considered in future research. Data we collected included blog posts and comments written mainly by individuals with BPD and limited to individuals who intended to disclose a diagnosis of BPD and publicly share their relationship experience, making it difficult to generalize our findings to other populations. Also, we could not be certain that all those who claimed to have BPD were accurately diagnosed after a series of tests conducted by the clinician. Future research could include in-person interviews with both partners involved in an FP relationship to extend the findings to the larger population, make sure that research participants are confirmed to be BPD patients, and examine FPs’ perspectives. It is also difficult to approach and reflect the point-of-view of FPs because they are hardly aware that they are someone’s FP unless told so by their person with BPD, who may be reluctant to confess their obsession toward them. Thus, further discussions are required to establish the definite concept of FP and fully understand this reciprocal relationship. Moreover, we did not consider other potential contributing factors other than a high RS level. Identifying additional factors that may allow non-TBPs to develop a healthier FP relationship with their person with BPD could help to develop an effective intervention to assist both partners form a secure attachment and establish a more supportive and stable FP relationship. Finally, it should be noted that we lacked access to additional and specific personal information beyond the data voluntarily provided in the posts. Therefore, no demographic characteristics or psychiatric comorbidities of those with BPD could be further identified and analyzed in the current study. Considering that BPD often coexists with other mental illnesses [1], it is possible that the presence of other mental conditions may have influenced the individuals’ symptoms and their relationship experiences.

Despite these limitations, this study was the first to address the FP-BPD relationship and apply the RS model and differentiate two RS forms to understand this dysfunctional interaction. Both individuals involved in an FP relationship simultaneously contribute to forming a long-term dysfunctional relationship and influence the relationship’s stability and wellbeing. This study employed the RS model to explain TBPs’ behavioral patterns that may interact with their person with BPD’s reactive responses, increasing the likelihood of their relationship becoming unhealthy. Our findings are novel and beneficial as we collected and reviewed actual data of real experiences reported by individuals with BPD and identified a particular relationship type they commonly have. They describe it as one of the most complex challenges as a person with BPD, but the FP relationship is rarely discussed. Thus, this study could be the first step to future research on the FP relationship, extensively on FP characteristics and more specifically on TBP versus non-TBP characteristics.