As with other personality disorders, the current view of borderline personality disorder (BPD) is based on a categorical model [1]. However, there is, at best, limited empirical support for this categorical conceptualization of BPD ^[2][3][7,8], which aligns with the argument that the thresholds used to diagnose many of the personality disorders are at least somewhat arbitrary ^[4][9]. This discussion has led to various arguments in favor of the adoption of a dimensional conceptualization of BPD that would recognize meaningful individual differences in severity beyond what can be captured by a categorical diagnosis ^[5][6][10,11]. This perspective also aligns with the view that there may be subclinical levels of BPD symptoms in the general population that may be linked with interpersonal functioning and psychological well-being despite not meeting the clinical threshold for BPD ^[7][12].

One approach to understanding the dimensional nature of personality disorders has been to use the Five Factor Model of basic personality ^[4][8][9,13]. There is clear evidence that each of the personality disorders can be conceptualized as problematic combinations of these basic personality traits ^[9][10][14,15]. This perspective has been applied to BPD such that it is viewed as primarily consisting of neuroticism with some elements of agreeableness, conscientiousness, and openness to experience ^[9][11][14,16], leading to the development of the Five Factor Borderline Inventory (FFBI) ^[7][12] and the FFBI-short form ^[12][17] to assess subclinical levels of borderline personality features (BPF).

Individuals high in BPF engage in various detrimental behaviors including non-suicidal self-injurious behaviors ^[13][18], misuse of substances ^[14][19], impulsive sexual behaviors ^[15][20], and physical aggression ^[16][21]. The potentially self-destructive behaviors that characterize those with high levels of BPF are believed to serve as problematic means to regulate their negative emotional states ^[17][22]. Given the nature of these self-destructive behaviors, individuals with high levels of BPF tend to experience lower quality of life and those close to them often feel burdened by their destructive behaviors ^[18][23].

2. Borderline Personality Features and Romantic Relationships

There is little doubt that romantic relationships are impacted by the interpersonal issues that characterize BPF. For example, individuals with elevated levels of BPF—and their romantic partners—report a range of aversive outcomes including less satisfaction, greater conflict, greater stress, more break-ups, and more intimate partner violence compared to those low in BPF ^[19][20][24,25]. Individuals with high levels of BPF tend to experience difficulties in balancing issues concerning intimacy and autonomy, which often leads to perceptions of rejection and unmet needs, along with feelings of mistrust, hostility, and anger ^{[20][21][22][23]}[5,25,26,27]. In addition, individuals with high levels of BPF often display intrusive, vindictive, and domineering behaviors in their relationships ^[22][26] and are often unaware of the negative impacts that their behaviors have on those around them ^[24][28]. These issues converge to create a situation in which the relationships of individuals high in BPF often involve an intense need for closeness and attention accompanied by feelings of rejection, distress, and hostility ^[25][29]. A pattern of conduct indicative of frantic attempts to prevent rejection or abandonment is one of the diagnostic criteria for BPD [1]. These actions could include mate retention behaviors (MRB), which are strategies that an individual can use to make it less likely that a partner will break up with them or engage in infidelity ^[26][27][30,31]. MRB can be divided into two broad types ^[28][32]. Benefit-provisioning behaviors are relatively innocuous acts that emphasize the advantages associated with the relationship to the partner and provide the partner with incentives to maintain the relationship (e.g., complimenting the partner). In contrast, cost-inflicting behaviors are relatively harsh strategies that involve imposing—or threatening to impose—unpleasant consequences on the partner if they were to dissolve the relationship or be unfaithful (e.g., threatening to cause harm to the partner if they appear to be flirting with someone else). MRB are characteristic of human relationships given the long-term adaptive advantage of maintaining monogamous bonds for child-rearing, but excessive use of these strategies can reduce relationship functioning and may even contribute to extreme partner violence ^[29][33]. Previous studies show that people high in BPF exhibit greater MRB ^[30][31][34,35]. More specifically, there is often a positive association between BPF and cost-inflicting behaviors, whereas the association that BPF have with benefit-provisioning behaviors tend to be weaker and less reliable. These results are consistent with findings that high levels of BPF are associated with the use of instrumental aggression in response to perceived rejection ^[32][36]. Because individuals with high levels of BPF have difficulty regulating negative emotions—including jealousy—they may also experience reduced empathy toward their partners, which may, in turn, encourage the use of cost-inflicting strategies that negatively impact their romantic relationships ^[30][34]. Although cost-inflicting behaviors can be effective in some situations, they are inherently risky strategies because their aversive nature may unintentionally prompt romantic partners to either end the relationship or engage in infidelity, which may perpetuate this destructive cycle.

3. The Importance of Trust

Individuals high in BPF often find it difficult to understand what others are thinking or feeling ^[33][34][37,38], and they consistently make more negative attributions with regard to the trustworthiness of other people ^{[35][36][37][38][39][40]}[39,40,41,42,43,44]. This pattern includes the tendency to make malevolent attributions for ambiguous or neutral behaviors ^[41][42][45,46]. These attributional biases likely contribute to a lack of trust in close friends and romantic partners ^[43][47]. Indeed, recent advances in the conceptualization of BPD suggest that issues surrounding trust serve as the fundamental core of this disorder ^[44][45][46][48,49,50], which is consistent with the finding that BPD involves high levels of antagonism (i.e., a basic personality trait characterized by trust issues) ^[47][51]. Trust is an essential quality that allows individuals to experience healthy and satisfying intimate relationships ^[48][52]. A general distrust in others may lead individuals high in BPF to act preemptively in an effort to avoid potential threats ^[30][34]. For example, individuals high in BPF may exhibit aversive behaviors when they fear being rejected or abandoned, which are issues that tend to be prominent in their thinking ^[21][31][5,35]. However, these aversive behaviors—including cost-inflicting MRB—may paradoxically endanger the relationship that the individual is attempting to save. For example, hypersensitivity to rejection may lead to increased criticizing, which, in turn, may lead the partner to withdraw and perpetuate the cycle ^[19][24].

4. Borderline Personality Features and Jealousy

BPF have been shown to be associated with jealousy in romantic relationships ^{[16][25][49][50]}[21,29,53,54]. These characteristic feelings of jealousy may be due to preoccupation with rejection and abandonment, which may lead individuals high in BPF to experience interpretive biases regarding the behaviors and intentions of their romantic partners (e.g., suspect that they may be engaging in infidelity) ^[25][49][29,53]. In essence, the jealousy that is experienced by individuals high in BPF may be due to their lack of trust in others. The intense desire for close relationships combined with concerns about rejection and abandonment—stemming from their lack of trust in others—are likely the reasons that individuals high in BPF tend to report disorganized attachment styles ^[51][55]. Although high levels of BPF have been shown to be associated with jealousy, the story is complicated by the distinction between reactive jealousy and suspicious jealousy ^[52][56]. Reactive jealousy is evoked in the face of undeniable evidence that one has been betrayed, such as in the case of witnessing one’s partner engaged in sexual behavior with someone else. In this circumstance, it would be completely reasonable for the person to experience jealousy. In contrast, suspicious jealousy arises in the absence of any clear evidence of betrayal and is predicted by lower levels of security and self-esteem. This form of jealousy is problematic because it can promote unnecessary stress and negative emotional states. It is important to note that jealousy cannot prevent betrayal on its own. However, jealousy can promote the use of MRB, which may help to protect the individual from the considerable costs of relationship dissolution or infidelity. Given the increased likelihood of perceiving others’ behavior as threatening (even when it is not), and given the intense fear of abandonment as well as the heightened reactivity of individuals with BPF in response to perceived threats, it seems reasonable to expect increased levels of suspicious jealousy for individuals high in BPF. There are gender differences in BPD such that women are far more likely than men to receive this diagnosis (i.e., 75% of individuals who receive a BPD diagnosis are female) [1]. In addition, gender has been observed to influence the relationships between BPF and certain outcomes. For example, BPF are positively associated with the use of the mate retention tactic of emotional manipulation in men but not women ^[30][34]. In contrast, BPF are positively associated with certain forms of intimate partner aggression (e.g., verbal aggression) for women but not men ^[53][57].