Help!!!!!🤐

Sooooo recently my mom started dating this guy and he has a son that's 2 years old than me.. He's beyond hot... But that's not the problem.. He keeps coming on to me.. Like "accidentally" walking in on me while I'm in the bath or shower... Constantly brushing up against me, makes dirty jokes..  Gets hard when I'm wearing shorts and a tank top And just the other day I swear I caught him jaking off to one of my pictures.... Like wtf?? What do I do?? I mean don't get me wrong he's extremely attractive and the horn devil inside of me is just like fuck him like he's never been fucked but then my morals side is just like that's gross your mom would kill you and he might end up your step brother.. I know technically he's fair game since my mom and his dad arnt married yet but what should I do??? If y'all were in my situation which would you do?!?