A hobby is a good thing, during our very brief separation I took up playing a card game I used to play as a kid. Turns out its become ultra competitive, so I started casually attending weekly tournaments. When W came back I made it clear I was going to do one tournament a weekend. W seemed glad to get the space. (afterall things were rocky at home). She'd get the rest of the weekend. Now that things are WAY better I still attend one tournament a week, and have decided to go pro so I have started playing online to get more practice. (don't worry it's not gambling).
The key of course is that W still gets lots of attention weeknights and for about 75% of the weekend. We still go out, have fun and other such things. I can tell she is pleased to see that I have developed hobbies that are separate from her. When we first married I dropped almost all my hobbies to give her time, and in true nice guy fashion this backfired on me.
I think it's great that he is getting back into hobbies, the question is can be find balance, and will he yield if GF ever pressures him about his hobby.