You tell the gym(s)

get off fml and call the police

Take a picture of him back and tell the police

Notify your gyms and the cops. Take a pic every time you see him taking one of you.

Date him and be obnoxious and boring. Trying to escape your stalker just makes it more thrilling for them, and cops won't do anything until after you are raped or killed.

He is not going to stop without at least a restraining order. Notify the gyms and call the police. Take pictures of him when he is around. Record him if possible with a safe app. Stay safe. Let people know what you are doing at all times. Text them when you’re home safe. Call 9-1-1 if he starts following you. Stay on the phone with the operator.

stop looking in the mirror

That depends on what you want. Do you want him to stop you following or do you want him to finally man up and ask you for a date?

There is this lady who gets great results by doing pantomimes of scared woman climbing the curtains, t-rex, secretary bird (the one that kicks its enemies) and Canada Goose. Or maybe it was hen, ostrich, t-rex and howling monkey. Anyway, you should try it, it looks fun.

Check if he slipped an airtag in your bag.