Do I need to pay for the flight ticket? Does he has the right to sue me? Part 3?

It's sad if he thinks he has a case. He cannot force you to pay back the ticket. Even if he brings you to court and makes up a lie saying "We had an agreement that she'd pay me back" it's pretty much your word against his, and since his case is so weak (and silly) he will lose. Sounds to me like he's throwing a hissy fit. Cut all communications from this loser. You're back home right?