In the context of borderline personality disorder (BPD), the behavior you described, saying "I hate you" and then acting like nothing happened, can be characteristic of the disorder and is often referred to as "splitting."
Splitting is a defense mechanism commonly seen in individuals with BPD. It involves a pattern of viewing people, situations, or even oneself in extremes—either all good or all bad, with little room for middle ground or gray areas. When a person with BPD experiences an emotional trigger or perceives a perceived rejection or abandonment, they may shift from an idealized positive view of the other person to an intensely negative one in an instant.
Saying "I hate you" in the moment of emotional distress reflects this sudden shift to a negative view of the other person. However, after some time has passed, the emotional intensity may subside, and the person with BPD may return to their more positive perspective, acting as if nothing happened.
It's essential to understand that this behavior is not a conscious manipulation but rather a coping mechanism arising from the intense emotions and difficulties with emotional regulation that are common in BPD. Individuals with BPD often struggle with emotional dysregulation, intense fear of abandonment, and unstable self-image, which can contribute to these extreme fluctuations in their perceptions and emotions.
While this behavior is considered typical for people with BPD, it can still be distressing for both the person with the disorder and those around them. Treatment for BPD typically involves therapies like dialectical behavior therapy (DBT), which helps individuals learn emotional regulation skills, cope with distress, and develop more stable and balanced perspectives on themselves and others.
If you are dealing with someone with BPD or suspect you may have the disorder, seeking professional help from a mental health specialist is crucial. With proper treatment and support, individuals with BPD can learn to manage their symptoms and build healthier relationships.