Why am i being this way?

ok well heres my story,ive been with my boyfriend off and on for 3 years. the reason why i say off and on is because he was a lil younger than me and he had his times where he would "cheat" on me with chics around his age. although he is into older ones mainly. anyway now we are living together and he claims he was "young and stupid" and he wont do that to me now and wants me to beleive him.. i cant . he has had a lot of female friends and that has always scared me due to me being cheated on almost every guy i been with. so one day he started a new job and after a few weeks he has been taking this girl home and sometimes to work and he wants me to be ok with it,well im not and heres why ..look what he did back then and two, well it so happens that i felt something was going on and be cause they were getting a lil too close he always got an attitude when id ask questions and he always said they were just friends. i set up a recording device in our bedroom so when i went to work at 230 am id see what he was up to. well he was up to no good. i heard him get outta bed soon as i lleft and i pulled away and some one came in.. i heard things that still get me sick to mystomach! i knew it was that girl because they were talking about work on this tape..i cant get over this!! wat can i do?? i made him stop taking her and texting her and even talking to her. i dont know if hes doing it but i now gotta talk to him on his way to work so i canhear if hes getting her and i feel like she is in his car at his breaks at work and i panic. i talk to him on the way home so i canhear also..we were so not like this ever!! now that this has happend we are constantly arguing due to me needing to know everything about him and calling him constantly and everything.. i dont be leive that he didnt cheat on me with her he denies it and he even heard what i heard cuz i made him listen ! he crys when i say someting about it and now its been 2 mos and im still doing this ..how can i stop and just trust him?? i want our relationship back to normal.. we were such best friends and lovers and now its like we hate each other... help me cuz i love him so much with my whole heart and i wanna beleive him,but i feel like theres something still there with them two.our sex life is almost non exsistant also cuz i feel like im not wat he wants and that i cant satisfy him any more.. i feel ugly now.. he just aint the same ,,my baby is gone.. help us plz