You have a three-month old - that‘s heavy and naturally limits your time for hobbies of your own, if you’re wanting to spend every spare minute doing things as a family when he isn’t golfing.
On the other hand, it sounds like your time is quite unbalanced. I adore my OH but don’t want to spend every minute with him. One of the things we love about each other is that we don’t have to - we can each take time out for the things we love as well.
It also doesn’t sound like he’s away that often. Half a day at the weekend (which is all you have really shown), and an evening a week is quite reasonable in my book. I’d want the same for myself. He could take the older one swimming or something in the morning while you have that time to yourself with the baby (if breastfeeding, if not, he can take them both somewhere or you could go out somewhere!) and then you take them in the afternoon while he goes to golf. And you still have a whole day in the weekend for family activities.
It sounds like the last couple of weeks have been an unfortunate convergence of one-off things (golf award, presentation evening, stag do)…not the way it would usually be.
As a note, could he car share with one of his golfing buddies so you aren’t always stranded without the car when he’s out, which would give you a bit of freedom with the kids every other weekend?
With regards hobbies - what do you enjoy? Reading? Martial arts? Art galleries? Gigs? Gardening? Brunching? Making papier maché models of famous European presidents? It really doesn’t matter what it is, just give something local a go and see if you like it.