Should I apologize to him?

Just forget him. He does not want a relationship, he only sees you as an easy score especially after he was cold to you but you still stayed over and had with him. He was being cold toward you because he probably does not want anyone to know about your ual relationship in case he finds another girl to sleep with. In the back of his mind he knows he's going back to Europe eventually and does not want a serious relationship. And he only brought up his sister to take the focus off of his own bad actions toward you and to make you feel bad (a similar tactic I've used during arguements). Get out while you can before you become more emotionally attached to this man who has no desire to be your boyfriend. Remember the saying "why buy the cow when the milk is free."