He's Depressed Over His Ex

I'm really worried.. but I have no idea if I should be. You see.. I hadn't heard from my boyfriend all day yesterday, so I got on AIM around 1 am and I caught him online. I automatically knew that something wasn't right.. he wasn't being himself, wasn't talking much at all.. wasn't happy. He told me he was sorry and was just really depressed right now. I asked what happened.. and he told me that I really didn't want to know about this one. I told him it was okay and I really wanted to know what got him down.. so he told me it was about his ex-girlfriend and it would only make me mad. I said as long as he didn't do anything.. it was okay. He told me he didn't do anything and not to worry, but what happened just got him so down.. he was almost crying. So, I just dropped the subject and told him he didn't have to tell me whatever it was. For the rest of the time I was on the pc though, he wasn't really talking to me and talking to like 4 or 5 of his friends about it..
So I was just wondering, should I be worried about what happened or what? I have no idea what it is.. and I don't want him to tell me if he doesn't want to, but I really want to know what happened.

Any advice?

Not at the moment but later, if he hasn't already talked to you about it, then ask him what was going on. After some time has passed maybe he will feel like talking about it.
Though I do agree with Britt
'Why is it okay to talk to his friends about it when he told you he didn't want to talk about it at all?'
Don't stress over it though. Things will work themselves out.

I don't really know much of his ex-girlfriend at all.. just that apparently, she really hurt him, I think by cheating.. =( He won't really tell me anything about his past relationships, he just says it's all in the past and doesn't matter anymore.

Yeah.. it confuses me that he won't talk to me about what happened, but he'll talk to his friends about it. I know it wasn't just him thinking about old memories because he told me that his friends were all asking him questions about it and things like that. He told me he just didn't want to tell me because it'd make me mad since I'm his girlfriend.. =( I still dunno what to do, I'm talking to him right now.. not even about what happened and he just seems all upset still.

Okay.

I'm not a big help in these kind of situations but from what I'm seeing is that he's hurt and he doesn't feel right talking to you about it because he's afraid that you'll do the same thing to you so he doesn't want to think about you doing it to him by talking about the situation with you.

Okay to explain it better

1` he gets hurt by ex
2` your worried about him and you ask him whats wrong
3` he doesn't want to talk about it because he might imagine you doing it to him if you talk about the past!

But he can talk to his friends because he knows that they aren't going to cheat on him like his past girlfriends because their his friends not his girlfriend.

I hope I at least tried helping.

Well the reason I bring this up is because when I start feeling depressed about my ex boyfriend I won't talk to my boyfriend at that time about the situation because then I start having thoughts that he's going to do the same thing and it'll only hurt as much and I'll feel even more depressed then ever. But I'll talk to my best friends about it because they'll stand with me through it all and the thought of them leaving doesn't cross my mind.

I hoped I helped! =/

I agree with ^

he probably stumbled upon something that reminded him of her, then thought about it, and was scared that you might do the same to him. [cheat on him] and now it seems he's putting a barrier up.

what i'd do in the situation is just tell him that you're sorry that she hurt him and assure him you'd never do anything of the sort. but i'm not you, so i just hope i sprouted any kind of an idea :]

Alright.. thank you so much, I totally understand that and you really did help me out a lot here. For now.. I've just been dropping the subject on it, it's already got his mind clouded enough and he's trying his hardest to get past this.. I have told him already, I love him and no matter what I'd never do such a thing to him. I've been cheated on before too and he doesn't deserve it and I don't want to have to go through all of that pain again.