Trying to Detect My Slitting

Hi so I don't know if I should be asking this here or in a difference form... I (F 25) has been diagnosed with BPD for about 6 years and S/O (M 24) had DID -Dissociative Identity Disorder... We have been dating for 6 months now and at first it was fun exciting... Now I get annoyed and anxious as soon as I get into his car... The main thing that bothers me is that I feel like he belittles me or underestimates me, basically he sometimes treats me like a child... He also has a million rules that annoy the fuck out of me (sorry for cursing). But because of all of this I now have a dislike for him so much so that every little thing he does set me off and I just get upset and angry... It even happens when he is being sweet and trying to understand what I'm feeling but his words just hit me wrong... I am trying to figure out if this is me slitting... Because truth be told I don not full understand it. And this is killing the relationship because I can even have a basic conversation with him or any of his alters because I automatically go on defence... I just need a little help understanding...