Why can't I leave my boyfriend knowing it's for the best?

I've been on and off with my current boyfriend for 9 months he broke up with me twice and I broke up with him the third because I heard he cheated on me. I would have asked him about it but since he hurt me twice I just didn't trust him and I knew he would probably deny it. Now we are back together. The first time we went out he gave me an excuse that he was having family problems so he didn't want to have a gf so he broke up with me after one month cuz of that. Then I found out he was in love with my bestfriend. the second time I decided to give it another shot but he treated me wrongly he never texted me, called and he pretty much acted like we weren't together then he broke up with me cuz he just didn't love me even though I have fallen hard for him. I gave him another chance because he apologized and told me he now realized how much he loved me and didn't appreciate me then but I broke up with him because of the rumors. Now we are back together because I just can't get over him and we talked about the whole cheating thing and he swore that it isn't true. we were crazy happy in the starting and I thought maybe this time things will change but now he's acting like he doesn't care again. We barely talk outside of school and I won't be seeing him for summer because he's going out of town for the summer. I love him so much and Im tired of his attitude and the way he acts I try to just give up on us but I can't . I hate how he acts and it's like am not his first priority. Almost none of my friends like him for me because of everything ive been through and i know maybe leaving him for good is for the best but its so hard. Please help :'|