Do not do anything if he doesn’t romantically approach you first. He is in a position of power over you and could easily spin this against you. Instead, if possible, act colder than you have been. Rather than smile, nod. Don’t talk unless you absolutely must. Leave classes ASAP. Drop hints if you’re seeing someone, but don’t allude to being interested in someone, because he may mistake that as you being interested in him. It’s a lot, I know, but there’s really no other way except to not engage.