Dating and Relationships Advice for Women

My sister start dating this older man and he was married i neva knew about that but i didnt care at that point but one day they start playing on my phone i thought it was her so i was playing rite bak but then i noticed days after that it was them together playing on the phone but this time it was only him i was shock but since i didnt want to be rude i continue to talk to him he made me laugh alot at his jokes and we talked about sex but we...