I need to help him, what should I do?

Okay, so my best friend is very lovesick right now, and I'm really starting to get worried. So here's the situation: He's always been a happy guy, really content and sunny all the time, but then this new girl moved into our neighborhood. He thought she seemed interesting, and I think that he really wanted to know her. She and I became friends really quickly, so I basically acted as a device so the could meet each other, I knew it would make him happy. They became friends really quickly, I always kind of knew that he liked her. He would always talk to me about it, because I've always been his best friend, he told me that he really liked her but he had no idea what to do about it. I would try to give him advice about what to say and how to tell her, (because I'm a girl too), but he never carried through. He's a good-looking guy, I know a ton of girls at school are crushing on him, but this one girl that he really likes doesn't think of him in any other way but a friend. He's NEVER liked anyone before, not like this, at least. So recently the three of us went to see a movie, I had to leave early. I'm still not quiet sure what happened, but he told me that he'd kissed her. Randomly, just out of the blue. he couldn't control it. She got really upset, said she wasn't ready for that yet, and they haven't talked to each other in months. He's just beating himself up about it, been trying to call her to apologize. I don't think she sees him that way, but I keep hoping for his sake that things will change. Partly, I don't understand because once she told me that she thought he was cute. I though that meant she liked him, but that's not the way it looks. I know something is wrong with him, he's never acted like this. He'll barely eat, barely talk, he won't even smile. He has this look on his face whenever he sees her, it's like he's actually in physical pain or something. I need to help him get through this, he's hurting a lot and it's not healthy. He's gotten to the point where he doesn't care if she likes him back, he only wants things to go back to the way they were. Please please give me advice so I can help him, he needs my support but I don't know what to do. Thanks for reading all of that, and thank you in advance.