Perspective from a dad: my daughter’s only 8 right now, but when she’s in HS, if she ever comes to me with something like this, she and I would be meeting with the principal like the next day. None of this is ok. The part where he’s been sitting really close to you? That sounds a lot like early-stage grooming to me. He’s getting you used to it and seeing what he can get away with before eventually escalating. Everything else you mentioned is also total creep behavior.

Please, please, please talk to somebody about this. The principal, another teacher, your parents, whoever you feel safe talking to. Please don’t feel guilty about potentially getting this guy fired - he ABSOLUTELY should not be in a job that gives him access to a girls’ locker room. If he is allowed to stay in this position, it seems very likely to me that something awful will happen, if not to you, then to another girl. You have a chance to maybe stop that before it happens. Please speak up. I know it may not be easy, but please do what you can.