Should he be able too?

Ok so I starting dating this guy last year, we knew each other for a month (spent like every day together) when I messed up. I slept with his baby momma and my ex bf. Shortly after I got back with my ex for a short period. Of course that didn’t work and I went back to this guy. I was starting to fall in love with him so one drunken night I told him what I did. He was pissed and it was hard to get him back but he took me back. We actually live together now, but he feels that since I did him so dirty and wrong (which I did I know) he should be able to do whatever he wants for a year or he can have two screws a year, and wants to fuck my bestie without me there. I feel like we are a lot more into this relationship that it’s only going to mess it up more. I feel that he’s acting like a damn second grader. This isn’t tit for tat!! help me!!