I love online games. I'm 15 years younger than the man in question, and have no children.
Even I don't play like he does.
It's great escapism. It's easy to get really involved in the quests (whether it's Wow or Eve or Skyrim) and you can distract your mind for as long as you need too. It's perfect for me, as a worrier, especially before scary operations etc. I play for around an hour or so, maybe 2 hours a day, when my anxiety is bad. DP either plays with me, or watches TV, or is out etc. We spend the time after doing something together.
Anyway, my point was, it's not gaming that ruins a marriage. But he's checked out of this marriage, and is using gaming to avoid either having to engage with his partner or split up from her.
Talking is a good idea, but make sure youve got a clear ttarget in mind. And it's worth being prepared for him to be quite harsh and willing to end things. If he's already said he isn't in love with her, and has no interest in trying to relight the fire so to speak, this relationship could be utterly hopeless.