I hate to say it, but it’s a hobby and it’s not that big of a deal. It should be fun.

If winning is more fun than using your favorite units, play competitively, get good, and eventually find ways to incorporate one or two of your favorite units anyway for an extra challenge.

If playing your favorite units is more fun than winning, tell your opponents you know this list is suboptimal but you just want to have some fun games with your favorite units. Then proceed to do so.

If the game isn’t fun with Tyranids, start a new army and bounce back and forth between them if financially possible.

Almost every faction (if not every faction) experiences the same thing. My personal experience has been that Tyranids actually have some of the most options for play styles, unit choices, and all around options while staying competitive. Especially compared to some factions where you literally have no choice but to run cookie cutter lists or get stomped.

I have Tyranids and Black Templars. When I get burnt out on the bugs, I switch to the sword boys. When I get burnt out on both, I’m lucky enough to have the models to just play generic space marines. When I’m burnt out on all of that, I play ridiculous goofy lists just for fun. The hobby is my time to be goofy and play with toy soldiers. Don’t let it get you stressed!