I dont think it my place to ASK to be invited....I mentioned it twice a while back that Im down to chip in on groceries, he knows Im interested...Im not gonna force anybody to be "nice"....Ive come to realize my roommate is selfish, I just try to ignore it.
Example: When he had an 
HIS LCD tv in the livingroom he would claim it as if he was a 5 year old. I would be watching tv in the living room and he would just grab the remote without saying the word and change the channel. I'd say wtf and he would rationalize it by saying its his TV so he can use it whenever he wants.
He amazingly also pulled this shit when 4+ mutual friends were over to watch a Laker game. When I put the Dodger game on the 32" tube TV (yes, 2 tvs in living room) so we could start the lakers game we had already delayed for an hour on tivo he freaked out. "My TV and I want to watch the dodger game! on MY TV"
150+ times a year he would watch a full 3+ hour Dodger game and then play another 4+ hours of video game baseball.
I finally got a bigger LCD to justify taking his out of the living room so I can watch TV in my own fucking house. 
When he had thrown those temper tantrums in the past I told him "fine, take over 
YOUR TV but sit on the fucking floor (I own the furniture)