I'm with CP: being an adult sucks because you have to take valuable energy and devote it to shit you'd rather not, leaving you less energy for the stuff you (selfishly) want to do.
When I started working 9 to 5, I pretty much quit gaming during the week for a while. Get home about 5:30 or 6pm, internet and worry about dinner until 8pm, realize I only have an hour or two to enjoy some games before the bed time rituals begin, realize that time constraint is going to prevent me from truly getting "in the zone" and deciding fuck it, if I can't play it my way (like an addict) I'm not gonna play at all. I'll just read forums and the internet.
This went on for years. Pine about my inability to enjoy myself during the week, then go way too hard on the weekend to compensate.
Here's what kind of changed it for me:
I came up with new routines. I started scheduling more of my time after work. Which sounds like the opposite of making things better right? Well not quite. For one I started working out (that whole self improvement thing you're talking about.) That took both willpower AND scheduling, because when you work 9 to 5, if you want to get something else important done you HAVE to schedule it. Leaving it up to feels and motivation doesn't cut it eventually. You have to push out something to make room for something. And the thing I was pushing out was the void where I would normally be gaming were I not feeling frumpy and unenthusiastic about it. So, about the only thing I lost was the time I was feeling weird and bad about not wanting to do anything.
I also started eating better, which necessitated scheduling ACTUAL time around shopping and cooking.
Between those two things and daily chores, I didn't have much of a day left to spend time on after work. I had less time to sit around feeling bored and maybe depressed, because I wasn't sitting around. If that were all that had happened, it would have been an improvement. But the best part about these new routines is....they give me a sense of completion after every day. I have tasks (that aren't work) that need doing, are making me better, stronger, healthier and once they're done......I've earned the right to fuck around. Games got their zest back because they weren't the other side of the coin from my job. They were a part of my daily or weekly routine, but a balanced part. Not my sole escape that I eventually wrung all the goodness out of until it too started to seem to suck. Familiarity breeds contempt.
Now, after doing my workouts and all the fiddly, healthy shit I picked up, I'm like "Yeah, I'm ready to game." Even if it's only for an hour. I went from having more time to game and being unenthusiastic about it....to having less time to game and being more enthusiastic about it.
On sticking with stuff, you say you quit when it gets difficult....but ask yourself what your goal is. Is your goal, your ideal, your reason for doing it what's causing you to give up when it gets challenging? For me working out has no concrete end goal, it is its own reason for being. Get healthy, get ripped....get more ripped, I guess? But like, learning an instrument, learning to program, learning a foreign language....what's the reason it can't be an ongoing challenge for you? That you succeed at sometimes and you fail at other times? Are you trying to learn just to learn, or is the learning part of a concrete goal you want to achieve?
Maybe the reason you're quitting when it gets tough is you're not actually committed to the thing you're trying. That you're trying it in obvious attempt to do something different rather than because it has actually inspired or interested you. We give effort to the things we want, whether that's people, things or activities, and when I'm not giving real effort to something the first thing I always ask myself is "do I actually want it?" Truly wanting something is what gets you through the tough bits, that's what working out and weight lifting has taught me the last year. It's just as applicable to video games though. We deal with learning curves in every game we play, but we put in the time despite the frustration and maybe embarrassment because we want to git gud at this thing. The process of git gud can even be fun itself. You just have to find something out there that you feel compelled to git gud at, rather than something you're just trying to git gud at out of boredom. I didn't get pretty good at painting Warhammer miniatures because I needed something to do, I learned (awkwardly, painfully, expensively) over dozens and dozens of hours because I was inspired by the pictures in the books and the models painted by the people at my local hobby store. I was compelled to paint figs even though my first....100? looked like such shit I felt bad about it.
Personally though I wouldn't ride yourself too hard. We live in an age where our reward centers get jackhammered minute to minute from every angle. When you are super-saturated by stuff, be that entertainment and the internet, sugar, caffeine, fatty foods, drama, newness and novelty, noise....and you stop getting stimulated, the crash is very real. Which is why when I started burning out on my preferred past times I went back to basics. Unplugged for a while, or at least gave myself stuff to do that broke the routine in positive (getting healthier) rather than negative (youtubing 4 hours away after work telling myself I was going to play something) ways.
But again, I'd find something you want to change, really change and try to introduce some routines around it. Take up a hobby (which I prefer to trying to go "I'm going to learn a skill!") For me, I wanted to lose body fat and build some muscle, and to burn off a lot of unused energy that was just going nowhere in my sometimes 10 hour gaming sessions. It doesn't even have to be about you, per se. Maybe you hate the color on the walls of your apartment. Maybe you've always thought your place would look a little nicer with some landscaping or gardening. Get a pet and take really damn good care of it, with walks and play time and grooming every day. Try to hang out with people (if you're that sort) you maybe stopped spending time with. Or try and take your gaming social with people instead of just doing SP games. I've been deep in SP games since before the start of the year and have recently got back in to some coop and MP games and remember why there's other kinds of game fun to be had besides the self-absorbed SP kind.