Should i just finally let it go?

wow..i was dating my ex for a year and a half.Everything as going great last year.After i came back from basic training in November, something changed.I discovered that he was posting pictures of himself on different dating and fling sites.He even started one the same day i left for training.He denied the whole thing and claimed that his friends and cousins did that.Then i discovered that this female was calling him and hen i spoke to her she claimed that they were just friends.So ever since then e ve been on and off..he started braking up with me at least 3 times a month..He claimed that he couldnt trust me and that i'm dating other people,which wasnt tru.So i moved to Columbia,SC for a little and he stayed back at home,which was like 3 hrs away.Long story short i found out that this female was texting him at twelve at nite saying that she cant see him cause shes at work..he denied the whole thing and claimed his boy used the phone and she thought it was him.So im back home and he hasnt changed..Since we've been together about 3 different girls popped up into the picture..jus recently actually..and they both deny trying to hook up,but she calls him everyday levaving messages..i dont understand why he has to lie.I never cheated on him and yet he doesnt trust me..is it time to let go??i love him but he is really emotionless.He makes me cry when he doesnt pay n e attention..i dnt undastand..