Struggling with Infidelity and Mental Health in My Relationship

I have had problems with infidelity in the past we almost every boyfriend I've had, I've never kissed or slept with anyone but plenty of flirting and emotional cheating. My current boyfriend and I have had some hard times and I have tried to break up with him so many times. whenever I wanted yo break up with him he would convince me to get back together with him. So that is where the racing thoughts and fantasies started. I used to think that anyone else would be a better boyfriend than him (he was/is very possessive, controlling and depressed). Now I know that that is not the case because everyone has problems and relationships are hard work. I have OCD, Bipolar and BDP and cheating and unstability can be a symptoms because of the lack of identity. I have been getting so much better and so has he but I still have thoughts of wanting to be with other guys. It has gone down a lot but he is still insecure about it and can get triggered easily. Does anyone have any tips to help strengthen our relationship?