I was in a long distance  relationship with a girl (I'll call her Mary. She started taking over my life and my time, to a point  where I was in my phone at family gatherings, parties, etc.

Not  only did she consume my time, she also started to try and stop some friendships, specificaly, this girl (Rebecca). We were friends since before I even started dating Mary, but the thing is, Mary hated her.

She  hated her with a burning passion, She'd wish death uppon her several times, called  her a Whore, a Slut, and several other things, but  Rebecca had no idea of this, since these 2 never even talked.

One  day, Mary and I had a fight about my  friendship with Rebecca. The fight ended with Mary saying something like "That bitch is dead to me" and I thought "Oh well, If Rebecca is dead to her, why should I even mention her?"

Wrong move

My  friendship with Rebbeca continued normaly for a few months, but I never told Mary about being friends with her, and I never told Rebecca that my gf wished death uppon her without even knowing each other(Rebecca had some self-love issues at the  time).

But Mary came to visit me once though

We  were having a nice time, when she saw Rebecca in the  distance. She asked me "Are you still friends with that bitch?", I told her I still was. She got real mad. We fought and cried for a while, until she decided to test me: Either it was her or Rebecca, couldn't be both.

Since  I thought I loved her, I had to talk to Rebecca and tell her the truth: my gf hated her and that we couldn't be friends anymore. She was devastated, and so was I. I talked about the  situation with my mom, and she said that if my girlfirend was setting up  stupid conditions like that, then she didn't love me as much as she  said she did. I told this to Mary and she got in the mindset that she  had fucked up, at least partially. She then let me be friends with  Rebecca, but still didn't want to know anything about her, but before that, I had to inform her that Me and Rebecca were going to see The Killers live, since the ticket was my brithday present, She got super mad but could't do nothing about it.

At  this point, my relationship with Mary was fucking me up in every way  possible, but that changed on the day of the concert.

Mary  and I didn't speak for most of the day, so, we went to the show and had a great time, mostly because Mary and I didn't talk that much during the day.

But as we were returning home in the van we rented to take us to the concert, it happened.

LSS, Rebecca and I made out.

At that point, I was already certain i didn't love Mary, not after all the shit she put me trough.

We broke up less than a month after that, she didn't knew I cheated.

TLDR  (Context is recomended though) : I cheated on my abusive, long distance  gf with my best friend she hated with a burning passion.

AITA  for this one? I hope y'all can help me out. Also, sorry for grammar mistakes, english ain't my first  language.