Last night, I [20/f] broke up with my boyfriend [21/m] of 5 years. Story inside.

This is going to be a long post, but I really do need some advice. I have no idea what to do right now, and the more people with advice the better. I'll also mention this a throw away, because I'm pretty sure my little brother knows my actual username and he doesn't need to see this.

Last night I broke up with my boyfriend. We've been dating on and off for the past 5 years, and we have been steadily dating for the past year. Before me and my boyfriend started steadily dating for the past year, we were both dating other people (I dated someone for 7 months, he dated someone for 9). The man [24/m] I was with used to abuse me physically, mentally and emotionally. He got me pregnant and I had a miscarriage, he thought I lied and had an abortion instead of a miscarriage. It was a seriously toxic relationship and he cheated on me while I slept in the next room. He would spit on me, slap me, throw me into objects, and call me every name in the book. When we broke up my (now ex) boyfriend was there for me. He helped me get over it all and it lead to him breaking up with his girlfriend of the time to get back together with me (since we've been on and off for 5 years, and all).

For the past 3 months, I have been feeling very strange about my relationship. I felt like I wasn't into it anymore, and that I was falling out of love with my boyfriend. We constantly argued and we always pointed fingers at each other, and never ever resolved any issues we had in our relationship. Now we used to have a VERY active sex life, but as soon as I started feeling weird about the relationship 3 months ago, my sex drive took a huge dive. I wasn't attracted to my boyfriend. I felt terrible and guilty having sex with him knowing that it wasn't the same as before. We used to have passionate and loving sex, and it had become awkward and painful. He noticed this too, and would comment about how something was up with our sex. I would just say I was tired, or I was distracted, stressed, sad, annoyed, you name it, I said it. About a month ago I stopped having sex with him all together. That was it for our sex life. We never showed much affection to each other after that.

We were that couple that always broke up. We would break up and get back together a lot, but always ended up "fixing it and staying together". Our friends stopped giving a shit if we were broken up that day or not because it became the norm. I stopped telling my friends eventually, and the only reason people know now is because I took it off Facebook (I never did the other times we broke up). Then my friends realized it was for real.

But here's where my problem lies.... I cheated on him. Mind you we only kissed, but that's still cheating. I broke up with him 4 hours later. I cheated on him with my best friend [21/f]'s ex [24/m] who she's still in love with. And I don't feel bad about it. And I know that what I did was wrong, but as soon as I was broken up with my boyfriend I had sex with my bestie's ex.

I don't feel guilty for cheating. I don't feel bad for breaking my boyfriend's heart, and I don't feel guilty for lying to my best friend's face as she tells me how much she misses her ex.

Now wtf do I do? Why don't I feel bad about this? Does it have something to do with my abusive ex? I don't really know what to do at all. I know I'm not a bad person, I have many friends and I'm well loved in my town. But why am I doing horrible things to the people I thought I loved?

TL;DR: Cheated on my bf with my best friend's ex boyfriend and don't feel bad about it. Help?

EDIT: spelling