I'm losing myself

I've been in a relationship with my boyfriend for close to 3 years. In the beginning of our relationship, he admitted to me that he had feelings for someone else. I brushed it off. He had this obsession with girls online that he didn't know/used to be friends with, especially the girl he admitted having feelings for. (he would look at her social media at least 5x a day but never looked at mine) I brushed all of that off and I honestly don't know why. Because I was in love I guess? He did the social media thing for a really long time before eventually stopping because I told him it made me upset. We had so many horrible fights about it and like I said, he did stop, but then would start again and we would fight, and then he would stop. It was like this for at least a year and a half. All while this was happening, my self esteem dropped lower and lower until it was gone because to me, these girls were so much better than me. Prettier, better body, better everything. So I started comparing myself to all these girls. Recently, he called me her name. (the girl he admitted to having feelings for.) but said it was a mistake and told me to get over it. That was in April. After that we were okay, no major arguments until now when I saw him once again paying attention to some girl he doesn't even know on Instagram. We have had that conversation so many times I was actually shocked that he did it.. and his excuse was that he didn't know.. which he always says. I feel like the countless talks and conversations and even fights that we've had about this literally don't and have never mattered to him. I feel he has no respect for my feelings at all. I try really hard to be the perfect girlfriend for him, but I feel like I'll never compare to these girls. I feel I'm not what he really wants. They are, and he just settled for me. At this point I feel so anxious going out in public with him because I always end up feeling so ugly and disgusting compared to all the girls he sees out there. I just want to jump out of my skin at this point.

I suffer from extreme anxiety and depression. I've been cheated on and abused before him. I have very little self worth and basically no self esteem anymore. I know what I wrote above probably sounds dumb to some but it really has affected my mental health, sometimes to the point where I feel so hopeless and like I deserve nothing but the pain I've dealt with in all my relationships. I don't know how to get better because I feel like i take 1 step forward and 2 steps back.. most people wouldn't even let things like this affect them, but I've been through so much mentally because of this, I don't know how much more I can take.