How do I stop letting my job define who I am?

Your whole sense of who you are is tied to your work, so when the job goes badly, you have nothing to stand on. A rough day at work becomes a rough day at being a person. That is a shaky way to live, because you have put your entire self on a single foundation, and any crack in it shakes everything. You are far more than your job, even if it does not feel that way right now. You are how you treat people. You are the friend who shows up, the parent, the person with a sense of humor, the one who keeps their word. None of that clocks in or out. The job is one room in the house of your life. You have been living as if it were the whole house. Start building the other rooms back up. Give real time to one thing that has nothing to do with work, a friendship, a hobby, a quiet ritual that is just yours. It does not have to be big. It just has to be yours, so that when work stumbles, you still have solid ground to stand on.