I can't say how many hours per week, as it does vary. He really, really enjoys gaming, and it's favourite way to unwind. He has a couple of friends who he plays the games with, so he doesn't usually game alone.
If he's off work, he will play during the day. I work from home, so that suits me tbh.
If he is in work, he likes to go on his computer in the evening, and he would happily play until the early hours of the morning. He comes down for dinner and will watch television or chat to me for a couple of hours. Then, he asks if I mind him going on the computer. A lot of time, I have things to watch on tele that he doesn't enjoy, I still have work to do, or I could do with going to see my mum/dad/grandparents for the evening. So, on those occasions, I say yeah no worries, go on the computer.
If ever I don't want him to, and I want to spend time with him - and I think this is crucial - he will stay downstairs with me without complaint. I don't think I could deal with someone who just gamed without any thought for their partner. At least my partner spends time with me and then asks if I mind. Usually I'm happy enough to have some me-time.
He plays two games mainly, one of which I play too (actually I play both, but the other I'm REALLY bad at so he won't squad with me ha ha) so sometimes I'll text him saying challenge me and we'll play against each other for a bit. It's quite fun!
And for those who said their partners don't game "because they're adults" that's bullshit. If you decide to stop having fun once you hit the age of 18, I pity you. Never stop doing what you enjoy because of your age, so long as it's not hurting anyone or breaking any laws.