I feel like shit😛

Guyyyysss i need help, my boyfriend and i have been having a lot of arguments recently because he wanted to be with another girl, which has been my insecurity for a long time, he asked me if it was okay with him doing that and i accepted, obviously expecting him to say that it was a joke and he only wanted me, but that didn’t happen, and they were about to do things (ykyk) but i begged him not to. The following days i tried to confront him and make him realize how bad he made me felt, but he kept blaming me i mean i know it was my fault because why tf did i accept but who on earth would ask for that having a gf? And he told me it was because I didnt gave him segs (i did, but i wasn’t in the mood sometimes and that pissed him off). Anyways, a few weeks later the same thing happened, but this time he didn’t ask for my permission, of course i felt even worse, besides the girl was supposed to be my friend even tho i’ve always had a bad feeling about her and i was right, she accepted to have segs with my bf even tho she knew i was his gf and she also had a boyfriend, again i begged him to stop and he did it, but this left me feeling awful. Since this happened i haven’t stopped comparing myself to her and it made me incredibly insecure, more than i was before, i think she’s better than me in every aspect and it kills me, what if he secretly likes her? Or what if they are secretly talking again? 

Pd: when i get back to school i’ll update and tell you what happens