Friend of the sister so embarrassing

Well that's a tough one! Caught ice cold and really upper embarrassing! The friend of my sister pulls my porn purely and as if that were not enough, no, he jerks off with pleasure. I was like thrust in front of the head, where is there something like that? What do I do now, how should I react? What if my sister shows up right away? This is really a delicate situation. Why does he put me in such a situation? And how should this work in the future? But first we have to clarify this situation now.