My friendship with my ex best friend had been extremely volatile since she got engaged (she is now married and we no longer speak). As soon as she got engaged, she began splitting me, blaming me for her own actions and getting mad at me for trivial things (e.g getting my own a Netflix account).It could be the case that I was no longer her favourite person but she would still become enraged if I spent time with other friends or if I didn’t adequately respond to a message in a timely manner. In hindsight, I was probably very much still her FP. 

Is there something about being in a relationship that triggers this behaviour?