TL/DR: try other hobbies, limit the sources of games you play, limit the amount of information about games you take in, force yourself out of standard playing habits and play types of games you generally don't like to break the monotony, take a break from games, just restart fresh on a game you've been away from too long because remembering what you were doing can be a big hurdle keeping you from finishing a game.

I have other hobbies I can get into so that helps but I go through phases of fatigue or disinterest with games because I play them all the time. Being good at multitasking helps for me because I can take advantage of doing multiple things at once to help stay current and avoid a backlog from building up. I can listen to music/podcasts while playing a game, I can read during loading screens or while waiting for friends to join in or getting ready in between big game runs, and I can read while watching a show or anime and keep up with both simultaneously. There are times I'll go an entire week+ without playing a game because my heart isn't in it but then I can 100% 3 or 4 games the next week. I made myself stop listening to podcasts about video games because I don't give a fuck about what other people are saying about games in general and most game podcasts I listened to weren't interesting enough to keep me from skipping to the next show in my queue and I've started enjoying games a lot more by keeping as little information about games from my mind until the last month before it comes out. A little piece here and there to gain my interest is okay but in depth information about a game before it drops almost always leads to a lesser experience once the game comes out. I don't care about spoilers, you can spoil anything and it's never affected my enjoyment of something so I've got that buffer to prevent me from being upset when I jump into a random thread and find out who the killer is from a game I've barely heard of. It also helps that I've limited the stream of games I've got to play. I was unemployed a few years back for a period of almost 9 months. I owned a ps3, an xbox 360, and a pretty good pc to play games on. I also had an active subscription to Gamefly for 2 games out at a time. Needless to say, I didn't leave my house much but my entire back catalog of almost 100 games was no more by the time a new job came calling. I'm not a collector of anything, it seems pointless to me... Just a bunch of shit taking up space and needing constant monitoring/cleaning that I never get any use out of because I almost never replay games. Nostalgia is not a thing in my heart as far as actually playing an old game again. I burn a game out until I know it's done and out of my mind for good. I got rid of my ps3 and 360 fairly soon after the ps4 came out because there was nothing coming out for either of those systems that I wanted to play that wasn't on going to be on the ps4. I also sold my vita to a friend and haven't owned a Nintendo product since I 100% Super Mario Galaxy by the second day I had it and sold off my Wii for a pretty nice profit. I'm down to the one console that all my friends have and that's a good thing. Just last month I realized I hadn't turned my pc on to play a game in almost a year and none of the games in my library were games I hadn't completed and modding Skyrim some more didn't sound like fun so I made the decision to delete Steam and my life hasn't changed and my wallet is now free from the tyranny of Steam sales. My friends don't even have pcs at this point because they don't need one anymore or they have something simple that couldn't run anything above ultra-low settings so having a limited supply of what to play has kept us more engaged in the games we have access to. I also don't play games on my phone/tablet because after about 5 minutes i get annoyed now at screen size/posture/controls so I'm really only a ps4 gamer now. Good luck finding what works for you, this is what works for me at least.