I know how frustrating it can be.... you explode, pick a fight, get irritated, feel abondoned.... and is it justified? No one can tell you when you are going to have these feelings overwhelm you and as people we are so vulnerable to negative emotions.

Are you in therapy? Medication alone isn't enough for BPD. I would consider looking for a DBT therapist.

In therapy you are taught ways to reduce these emotions and stay in control, such as, accumulating positive emotions, building mastery(do one thing a day that makes you feel competent and in control), coping ahead (create a plan) and lastly taking care of yourself (get enough sleep, eat right, exercise, no drinking)

There seems like there is a lot of history in your relationship, rebuilding trust on both ends takes time. i hope everything works out for you guys.