Please HELP: My Man is Openly Cheating On Me

Hey Readers.

 I'm in a situation right now and i need your advice. I have been in a relationship for 3 years now and things haven't been so great but we thank God. 

This is my first long term relationship and am surprised i stayed this long .I'm the type of girl that doesn't fall in love easily but this time i did. Well straight to the point, my boyfriend is seeing a girl that he claims he asked out 3 years ago before he asked me out. 

The first time i found out ,i was so pissed and decided to end the relationship but he begged and even called his father to plead with me.He called the girl a bitch and all sort of negative names and promised it would never repeat itself. i forgave him because i spoke to his dad and he assured me everything would be fine.

I have found out so many other times that hes still seeing the girl and this time i have had it up to my neck. We recently moved to a new apartment and after we moved i travelled home. I'm back now and i snooped in hisphone. i found a video of him and the girl in this our new apartment which means his still seeing her and brought her to our new house.We stay together in the same apartment and i know about all his movement so whenever am not in town he's always hooking up with her. I'm totally fed up about this matter. when i confronted him about the issue he said he cant 

cut all connections wit the girl and moreover hes a guy and he can do whatever he wants to do so if am planning on doing anything i can go ahead and am the one that would loose. i have made a lot of sacrifices that has affected me both positively and negatively and put a lot of efforts into this relationship and i don't know what to do about it anymore.I'm not the type of woman that confronts a girl over a man because i believe the problem is from the man cause hes staying in contact with the girl which is giving her green light.I'm totally fed-up, Please i need your advice....