Hey Z,
This really sounds like a perfect 'male mid-life crisis syndrome' description.
Your life is kinda drifting away from you.
You did all the right things, and all the things you were supposed to do. You even have some results to be rightfully proud of and yet, you are turning into a slightly embittered, depressed and disoriented man, you have never been and hoped, you would never be.
As previously mentioned, you need to define your own sense of happiness. The old model of 'what happiness meant' from your 20's and early 30's will not do anymore. You have changed and so should your own definition of personal happiness.
Only you know yourself. And only you can really tell, what makes you happy. If you do not know, you need to go on a journey of self-exploration. You need to try new things and see, how you feel about them. Be prepared to make a few mistakes and learn from them.
My old folks used to be very 'social people'. I cannot remember the times we lunched or dined together without having at least half a dozen guests dining with us. Obviously, I hated that being a kid. Later on, I started playing with the idea that it would actually be a very nice idea to host a dinner or two for a few friends. Nope, it was a total waste, I hated every bit of it. I was simply not meant to be a gracious host. Whatever. But I did like the learning part.
I have always been a generous person by nature. I must have picked the right parents and gotten lucky later on, so that I was always able to finace that generous attitude of mine. People around me started taking me for granted and started believing that I was some sort of a good-natured fool. I quickly changed. I always paid my drinks and pointedly invited the others to do the same. They were pretty shocked; they did not like it. But I did. I got rid of the guys, who were mostly in for a cheap ride. It did me quite some good.
I have learned how to work for my money. I have also learned, how to put that money to work for my happiness. Both my BF and I budget generously for our vacations. We are on the go, purely for fun, for some 75-90 days every year. We work hard and we play hard, if you are catching my drift.
Your life needs ever changing contents. And people around you to share those contents with. My BF and I are a bit of 'museum queens', so that part works just great for us. We also are into nature tracks and though, we do not overdo it, you'll see us climbing up and down the hills and the gardens, parks, wherever there is something, we can comfortably do in one day. At times, we are just lazy and spend a day or two reading our books, making all kinds of silly notes and yeah, planning other trips.
I'd love to get a non-commercial flying license for a small plane and will probably manage to do that next year. My BF says, I am completely mad

and should not be allowed to do anything of the kind. So, he'll be reading his books and I'll be hopefully flying my small plane around. You do not need to share everything with someone you love. Sometimes you do your own thing and he does his own, too.
No one has got a ready made prescription for your personal happiness. You have got to come up with your own ideas and concepts. Everything other people can do for you is to share their experience and offer a few pointers.
Good Luck.
SC