I'm At A Loss.

I'm horribly in love with my boyfriend.. and I wish I wasn't. He is great to me.. when he feels like it. I don't know what his deal is, but he gets in these horrible moods set off by the smallest things to literally nothing at all. He treats me absolutely horribly when he's like this. He ignores me, yells, acts like everything is my fault, tells me we should just be over.. and all that kind of stuff. I try to talk to him about it but it never goes well. He just does what he always does and denies it, yelling, degrading, ignoring. Now, I consider myself to be pretty down to earth, so when I say I'm not provoking this I mean it. I try to work it out, ask for ways we can compromise and such, and nothing ever comes of it. Recently, he accused me of breaking plans with him (which I didn't). We had plans and someone else invited me to do something the same time. I told him to let me call them back and tell them no since we had stuff to do. He then started yelling and saying that I wanted to go with them and not be with him and he couldn't believe I was breaking our plans. He still to this day insists that I was planning on going with them. Needless to say, after I was done begging for mercy, he calmed and said that breaking plans was huge to him and was a horrible thing. Funny thing is, he constantly breaks plans and promises himself. ALL THE TIME. He says he will do something and never does. He will leave me waiting for over an hour and then change his mind when it comes time to do it. I tried to bring this up, but he won't listen. All I get is "whatever.. whatever you think.. yupp sure". Now, aside from this horrible once-a-day attitude, he's great. He's a great boyfriend and truly shows he cares for me. He makes me feel wonderful and says he wants to be together forever. I can't leave him.. So please don't suggest that.. but I'm at a complete loss. I get treated like this sometime everyday. I tried talking, yelling, ignoring.. I just don't know what to do. I have thought of bipolar disorder or stuff like that, but I could never bring that up. His friends are extremely loyal so I don't know if I could ask one of them if this was normal before we met. Also, I don't think he would ever hit me. He grew up with that in his house and swears he could never ever hit a woman (I know about growing up around it = better chance of doing it, but he seems very admant and sincere about this). I just need some advice, or even someone who could relate and tell me it gets better? That it can work out? I can't imagine my life without him and never want to have to.