I walked in on my mom doing it with my gym teacher...?

I would be sure to tell your Dad!!!

Wow! That's a powder keg ready to blow up! Start with mom and go from there... Anyone else you talk to will lose the gym teacher his or her job, still, it was very inaproppriate and unprofessional. Unfortunately anything you decide to do will cause your home to be traumatized. You do need to do something though, it is not healthy to hold it all in, on issues like that! There is no good answer and I am so sorry that has happened to you!

Take care and be safe, know that there are people here who really care about you!