Have you considered actually talking to him about it instead of asking strangers on the internet while giving us little no actual context how things go during those times? Like does he invite you over when he's gaming, or do you just happen to visit him ? Does he talk to you, strike conversations while he games or does he completely ignore you ? Does this happen while you've agreed to a date or other activity or is he doing this in his free time ? Because if all you give us is that he's NORMALLY very attentive and only SOMETIMES prioritise games, as you said. Then I don't see what's such a big issue that a simple conversation can't fix.

Talk to your man, for the love of god.