Don't Know What To Do Anymore...

Me and my boyfriend have been together for a year now, of course during the honeymoon stage everything was great. It started off as a long distance relationship, he was in Cali and I was In Arizona. After two months of dating he came down to visit me. It was great, when he left it was heartbreaking for the both of us. We would Skype all the time, etc. Then we started fighting, over little things. I guess because we missed each other so much and stress from school and work. But after 4 months of not seeing each other in person, he finally turned 18 and moved down here with me! But it wasn't all that great... He was happy at first all on the phone, etc. But a week into it, he started becoming more distant. In public, he would walk away like we were nothing more than just friends or strangers. He always looked despressed when he was with me out in public. Then I'd always ask what was wrong and he's of course say nothing. That his head hurt or he was tired. But all the time? I haven't done anything to him to make him upset with me. So It sucks, my self esteem lowers more and more because of how he treats me in front of other girls, he'll leave me alone when they come around but rushes back around, super affectionate as soon as a guy takes one look at me. I hate it. I always tell him what bothers me and that he needs to work on it or we won't make it... Of course he tells me he will, blah blah blah all these empty promises. He never does, and if he does change something it only lasts for a week or less and he goes back to it. He's always on his phone as if he wants a distraction from me and ugh there's so much more. But long story short, I always tell him if he doesn't want me anymore or isn't interested in me or working with this relationship he can go home. And he always say no, I wouldve left already if I didn't want you, etc etc. So I don't know what to do, it's constant, he tries to impress people by acting dumb towards me. It doesn't work but he thinks it will. He never listens, etc. But he says he loves me, wants to marry me, etc. I'm stuck in this stupid confusing situation. I don't know what to do. I love him more than anything. He was my first, the first one I was able to trust, etc. What do I do?