Do I Walk Away or Keep Fighting?

I dated my ex for 2 and a half years, until we ultimately broke up in May. Our relationship was a mess between each of us cheating, but still stayed together. We broke up after an issue that we both should have dealt with, when he just completely bailed as far as physically being there for me. In July, we started talking again, and spending time together. I've used these past several months to try to fix my past mistakes by being there for him, being loyal, supportive, honest, and open with my feelings. Meanwhile, he's continued to speak to other girls, hang out with other girls, and blatantly hit on them on Twitter. We're not together, so I just take his word he really loves me and isn't going to talk to anyone else. He says he just needs to focus on himself, and get his life and future together, and he doesn't want to have to feel obligated to be there for someone else, or have to be pressured for anything. He says he loves me, and I tell him I love him and miss him all the time. But with all this "cheating," and empty promises about spending time together only to be ditched for his friends or work, is making me think he really just doesn't want to be with me....not "anyone," and this is just some game until he finds someone else. I really love him, but it tears me apart when he says he doesn't want to be in a relationship right now, cause he needs to get his life together and be happy with himself; I think this is just an excuse, and he just can't say he doesn't want to be with me in the future.