Thanks for the advice!
I shared it with Thunder and the rest, and we're talking about it a bit.
@Ariakas: You're exactly right-- I'm looking for an "in the middle" compromise that makes everybody comfortable. I'm most concerned with how Thunder's behavior and attitude while he's upset tends to upset everyone else and is in general, hurtful. If you would like a more specific incident to analyze, the latest one is a really good example.
Ariel, Vegeta, Company, and I were all taking a shower together and in general fooling around while Thunder and Andulvar were driving around and hanging out. Thunder was fine in the morning. When he comes back home, he is most definitely not fine. When he's moody, he doesn't look at anyone, doesn't really respond to anyone beyond the "nothings" and "fines". He begins cleaning the place up furiously, and proceeds to sulk in his room with the door closed-- another occurrence saved only for his moods.
So I took a walk to the grocery store with Ariel and Vegeta, and on the way back, Ariel decided that we would get Subway for dinner, and make dinner for Company and Thunder when we got back. We didn't call or tell Thunder this, who was at home being moody, or Company, who went to Andulvar's place. Company didn't really care, and Thunder didn't show anything but continued moodiness, keeping himself in his room. This was fine by most of us, even though we wanted him to explain that he wanted alone time instead of acting that way to get it.
Last night, everyone went to a play. On the way there, Thunder and I began talking (he was in a much better mood then) and he began explaining what had been wrong with him. A lot of it was still jumbled, but I was just happy that he could talk about it at all. I told him that the way he acts when he's upset makes everyone unhappy and it's hurtful, and he proceeded to tell me that he knows, he's always known that. That it's "just the way he is."
That statement would be fine if we were still just friends. If we were just friends, I could go hang with someone else and not have to deal with it, because it wouldn't be my problem. But instead, I'm in a relationship with him. Being upset about something and needing time, I can hang with. Shoving people away like that, I can't.
@SNeacail: That it's EXACTLY! It kills me! What's wrong with guys that they have to do it that way?! I don't understand!