Lately, my boyfriend doesn't seem to want sex. Even when I try to initiate it, he just doesn't seem interested, and it's so frustrating! He also seems to be pushing me away, like he'll tell me one day that he wants me to go over, but then he changes his mind, and he never seems to want to come over here. He claims that he's "tired" but he doesn't work or do anything that could make him tired ya know. I've kinda had a feeling that maybe he could be messing around with someone else... like lastnight he didn't answer his phone, AT ALL, and after I called him a few times, he turned his phone off, then today he claimed he was sleeping, but it was only 8pm, which isn't normal for him. Then today, I was on the phone with him, and I heard his cell phone ring so he told me to hang on so he could answer it, and about 5 minutes later he comes back. I asked him who it was and he said that "I don't know, they hung up when I answered, I tried calling back but they didn't answer either" but it doesn't take 5 minutes to do that. He has cheated on a past girlfriend, and he told me he did so because she didn't treat him right. He's told me that I treat him great, but nevertheless, he has cheated in the past. So what should I think? Am I over reacting? What should I do?

Ditch him. A tiger doesn't change his stripes. If he has done it before he will do it again and from the description you gave it sounds like things are adding up when he gives you some pretty goofy excuses.

I also agree with Nunnzie. But I know it will be hard for you because it sounds like you like him. But it will be better for you in the long run and you will meet someone that will like you and only you