The guy is lucky with his sister - she is a nipple. She's ready to open her mouth for him to stick it in her. Apparently she serves him regularly, because he no longer feels affection for her, but fucks her like a street whore - rough and bold. However, she seems to like this treatment.
How all the girls love young tutors, they apparently drool at the sight of these men with pumped arms, so they give him all the passion, in principle, not surprised.