I'd suggest playing games together that are calming and that he can play purely for fun rather than "trying to win" like an elitist. I know that I've had an elitist mindset in three games in my lifetime, two were co-op FPS with my little brother while growing up, but we both made mistakes and I noticed my anger early enough. The 3rd game was Starcraft II, meant to be 1v1 in ranked play. Games with more than 2 players are generally considered just for fun. When I made that connection I was able to take it less seriously and just have fun with friends when playing, rather than to win.
If he can't make these connections himself, and to notice that the goal is that he gets to play /with you/, rather than win at everything, then the venue needs to change - try games that are less intense and involve co-op or maybe are MMORPGs. I would say Overwatch because of how much my friends and I can take it as a fun game - capable of feeling like a normal FPS, but also including abilities that make each hero fun and unique, but he sounds like someone who would take it super seriously and you'd be back to square one.
Maybe a game like Portal 2's Co-op! Don't Starve Together if you like that style of game. Look up light-hearted, low intensity games!
P.S. You say he wasn't like this during the 1st year. Just a thought, but often times when there's something large bothering you underneath, the smaller things set you off easier. Maybe there's something digging away at him?