What should i do about my boyfriend who's cheated on me countless times?

I have been in love with my boyfriend for4 years (he asked me out a year ago hes my frist) i was 1 of his bestfriends b4 that time of 3years so i heard about all his crushes even though he knew i was in love with him he still shoved it in my face most of the people he said are my friends that i loved and trusted who did the same thing even asked me to help them get him they knew2but im not getting into that long storys so anyway for the year we went out he continued this behavior as did my friends flirting cuddling kissing everything! everytime i confront him he says im being paranoid that he does nothing overtly ual and he keeps bringing up this1girl that he compares me2and how much better she was that she never complained or said what he was doing is cheating my friends say the same thing and now he says hes seen what hes been and he wants me to forgive him i love him i cant live without him but it just seems to painful knowing what hes done i just cant trust him what should i do