INFO: You say your family is well off, but exactly what does that mean? Are they independently wealthy? How reasonable was your expectation that he could afford that specific car, or that he really meant 'any car?' I'm assuming you didn't ask for a Lamborghini because you knew that wasn't on the table, but you did ask for a high end luxury car.

I'm quite well off and probably couldn't afford that car for my kid, nor would I want them driving something that expensive, that presumably I'd pay to charge and insure for a new driver. When he said you "couldn't seriously have expected him to buy a 17 year old a real brand new BMW," that may be a valid response.

He's still buying you a car, so weather or not he's breaking his promise kind of depends on how reasonable your expectations were. It sounds like he set you up top have high expectations so he could deliver the punchline, and didn't try to make real plans with you over these 9 years. That's a very shitty thing for him to do. He knew you'd be upset. That definitely makes him an asshole, but that info is lacking a bit in the story.