SURPRISED!!! I find my stepbrother masturbating with my panties, I discover him fantasizing with me his stepsister

I came home early from college and I find my stepbrother masturbating with my underwear, the very dirty one gets excited seeing my lingerie and left my panties full of his semen. It bothers me that my stepbrother does not respect my privacy, to teach him a lesson I masturbate in front of him although I do not allow him to touch me, he must understand that I am his stepsister and we can not have sex.