Help relationship issue \:?

Me n my boyfriend (who is now my ex) of 3yrs started fighting alot after we got back together from our "break" we were good the 1st few days but then it went dwn hill we broke up Mutally because I thought he was acting different over army stress (he is leaving in a month ) and we were suppose to get married when he came back but after we broke up he was being mean as he'll to me Kirk telling me to shut up that I needed to mind my ****** buisness and things like that then my friend showed me his twitter and he likes a girl in one of his cles were freshman in college (we don't go the same college) I was so hurt I gave him all his stuff back but he told be he loved me and I told him I wanted to get back but he said he wasn't sure about what he wanted and my grandparents now hate him cause he's cheated on me once before and has begun smoking Which is a turn off and he still trying to communicate with me but I'm positive he is still talking to the other girl what should I do?