Hello and I am sorry you are having issues. I agree with Karen your therapist has the right reasons for your behavior. IMHO you need to see your therapist often as verbal and physical abuse to your b/f is unexceptable and your behavior is becoming abusive. You may have some underlying anger management issues going on too.
Perhaps you need to apologize to your b/f and only keep the conversation about the apology. Do not let it turn into a debate of why you acted as you did because being slapped for any reason is not something most people are going to accept excuses for. I am sure you are sorry but you must come to terms with your feelings in order to have a meaningful relaitonship.
No way am I judging you, you have a illness and when our illness gets the best of us we must be proactive in getting help.
Coming here and talking is one good way to vent and connect with others that share this disorder. I am glad you are here.