AITA for getting angry at my friend for not inviting me to play a game

I have an internet friend who shall be called Retro who has been for a good amount of years. We met via a mutual friend on discord and primarily talk using facebook as it is the social media of choice in my country which he is also in. Now Retro and I are close, we have the same interests, namely anime and gaming. We send anime pictures to each other and discuss stuff we like and dislike, you know, the normal stuff friends would do. I thought me and Retro were tight, I usually keep personal problems to myself, but I learned to open up to him if just a little. I've always looked up to him and thought we were the best of friends.

Retro isn't exactly fond of League of Legends, he used to play a lot but he got fed up with the games and the teams and such. Whenever I invite him he refuses and that's that.

The other day, I spot Retro and another person on discord playing League so I join in and we have a grand old time. I tell him on facebook to tell me when he wants to play next time.

The following day, I log on to discord and see Retro and a different friend playing Warframe and opt-out of joining the call because I don't play Warframe anymore. After a few games of League, I check discord and see a handful of people plus Retro readying up to play League. I join the call and ask if I can join.

"Sorry, we're full", Retro said.

That broke my heart, man. After hearing that, I leave the call and play a few games of League feeling sour. After that, I did the "ignore messages" thing on Facebook because I don't even want to talk to him now.

Am I being too clingy here? Is getting angry at him for being in a full party justified? I don't want to get angry at what I thought was my best friend, but I'm considering cutting him off because this is not the first time Retro's done something like this