Why do I keep fixing everyone's broken things—and resent it?

You can fix almost anything. That's true, and it has made you useful — it has also made you tired. Every broken thing in the group finds its way to you, not because you asked for it, but because you never said no. This is not a skill problem. You already know how to fix things. The problem is that you let your competence become an open invitation, and you started calling the exhaustion patience, as if wearing out quietly were a virtue. Your team cannot read a limit you never spoke. They only know what has worked before: bring it to you, and it gets solved. If you want this to change, you must change what you do — not wait for them to notice you're tired.