He sounds horrible! (at the moment!). I don't think you should stop playing games completely as he really needs your help in learning how to play nicely, otherwise he will struggle to hold down friendships if he behaves like this with them.
I am sure I will only be saying things you've already tried.... But I guess I would wait for him to ask to play a game. Then talk to him very sensibly about the fact that you would like to play with him, BUT his attitude in previous games has made you unsure about doing so again. Ask him if he can promise to enjoy the game even if he loses... Point out that in any game only 1 person can win, 1 person will come last etc. Ask him how he feels when he's losing... And then point out that when he's winning, that means someone else must be losing, and they must therefore feel just the same as him... And how would he feel if they stopped the game because they got cross, angry etc. He'd miss out on his win and no-one would end up happy.
Explain that most games are down to luck - roll of a dice etc. So wining or losing really doesn't mean the person is a hero/fool etc.
Is he insecure? Why does he get so upset about losing? Do family members tease each other if they get things wrong/fail? Or massively praise a winner?
My SD was terrible with games, sounds like your son! She is an only child and hadn't had much experience of playing with kids her own age. Just adults, who are either naturally better at things than her (eg basketball when she'd throw a hissy fit if she didn't get as many baskets as her dad
) or who 'let her win'. Now she's 12 she is so much better, but it's taken a long time to reason with her and get her to understand other people's points of view. I'd still avoid playing snakes and ladders as the number of highs and lows are just too much to bear 
I think empathy has a real impact on how children are with competition. A friends child is so sensitive and empathetic she would lose on purpose to avoid someone else losing
. Think that's too far the other way!
Keep going at it. If he starts being difficult, stop the game and say you'll carry on tomorrow when he's in a better mood. Be kind if you can see he is really trying to keep his emotions under control. Praise people for trying. My DH always says 'good game' or thanks for playing or something similar after every game, with a handshake etc (v American, but I can see it seems to work) whether or not he wins or loses.