Am i being stupid?

I have been with my bf for 2 years, we were very casual at the start and we split up last summer for 6months but got back together. He seen a girl during this time and done this with her that he never done with me like go on holidays. I get cross when I think about this. Also i have recently checked his emails and he is talking to other girls and suggesting meeting up with them. Even though i am a strong person i can not seem to end the relationship, when we are together and do stuff everything is fine but i can't seem to forgive and forget? Should I end the relationship or wise up and give him the benefit of the doubt?? Its driving me crazy

Hey hun

if u 2 r back 2getha y does he want to meet this girl... if i was u i would of dumped him hun.. but then i know how hard it is when u love someone.. but if there is no trust then u shouldnt be with him..