I have a gamer husband, and if we were ever in the same sort of situation (ha! I've tried playing COD in split-screen mode with Mr. J, so that he could practice shooting a moving target, and even just trying to run around the terrain made me look like a spastic idiot. I have a great deal of respect for anyone who is good at these games.) then the conversation would have been much different:
Mr. J: We're in a full lobby so don't bother waiting for us for a game.
Me: You're saying you're playing without me? I asked you to play so we could play together.
Mr. J: Yeah, but I logged on and [Friend] and [Buddy] and [Pal] were already in a party and they invited me so I joined.
Me: So you're playing without me, after I asked you to play with me? (Yes, I would probably have to reiterate this - for some reason my darling husband sometimes turns into a clod when a game console powers up, heck if I know why.)
Mr. J: I can always back out and play with you.
Me: Yeah, go ahead and do that, tell the guys I said hi though.
I think your "Well, then I don't want to play at all" was very "I'm taking my ball and going home" immature without giving him the opportunity to try to fix his obvious mistake.
So you two were going to play a video game together in separate rooms of the same home?
If you don't have a gamer in the house (and this would be compounded by having more than one) then I can see why this would be difficult to understand. But you can only have one console active per TV*, and the vast majority of households don't have two TVs in any one room. From what I can tell, even Sheldon and Leonard only have one TV in their living room. In order for both members of the Dark household to play the game together, they have to be where the TVs/consoles are. No, it's not ideal. But it's what works.
(DM: Mr. J is very jealous of the two XBOXes and of the fact that DarkBoyfriend has a partner who plays games. Oh, but he still loves me.)
*Yes, split-screen is possible but it sucks. When the option of two separate consoles exists, that will be the preferred set up every time.