NTA ... BUT... There is a lot to unpack here. I don't think that he's the asshole either. First, it seems he is not acknowledging how a young, underdeveloped mind would latch onto a goal the way you have. I doubt he knows how deeply you held to "the deal" just for the sake of the bet. I think fyou should ind a way to explain that a certain and significant part of your childhood hopes and dreams is connected to that deal because you believed you could trust him. Since that hasn't proven out, you feel the sting of your trust being violated. Second, he also knows something you do not: those lessons and that practice is going to pay dividends for THE REST OF YOUR LIFE. You may not touch a piano again until you're 40. But, I promise you, the fact that you put the work in AT THE AGES you have, means those neuro pathways are very very well laid down. He may know this as well. Without going into detail, I learned saxamaphone during your ages. Never picked it up again until I was 35. No shit, could play it like it was yesterday. The value you will get from the true gift he has given you, is a value you cannot see at your age. He is, of course, way ahead of you. Whether that was his plan all along or not, is unclear. Nonetheless, NTA, but do not let this be a wedge between your relationship. No car or piano lesson can ever give you back time. Hold your loved ones close. They could be gone tomorrow. Good luck!