So, my friend pressured me into coming overseas with him. He mentioned that he wanted to travel with me, and I said that it would be awesome, so to cut a long story short, he locked me in his car and said "am I buying you a ticket or not?" I told him I can't go because of exams, and he said "that's fine. If you can't go, you can't go! We'll just refund the ticket." So a few weeks went by and I told him I can't go because I have to sit exams during the dates we were away. He got mad, and said I have to pay for the ticket now ($800) because he bought NON-REFUNDABLE ONES!! He's been pestering me for weeks for the money but I clearly told him that I may not be able to go and if that's the case, we will just have to refund the ticket. Should I pay him back, or should I not pay him because he was stupid to buy non-refundable tickets?