Is this the wrong thing to do?

My boyfriend has an associate's degree in music and he wants to go into instrument repair, which I think is a dead end. I've told him this on many occasions and I have suggested continuing his degree and pursuing a career in music education, but he still is intent on going into repair. He either would need to learn on the job or go to a trade school. There are only six trade schools in the country and none of them are located anywhere near us. I don't think the trade school would help him any more than getting experience on the job would, but I still think he would be very hard-pressed to find success in this field. I've even suggested just taking up instrument repair as a hobby that may come with another, more successful job, but I don't think he's convinced. He knows exactly how I feel, as I have expressed this to him on many occasions, but I'm worried that he won't take my advice. I don't want to stay with him if he goes into instrument repair because I honestly don't think I want to be with someone unsuccessful or see him throw his other talents away by making a poor decision. Is it wrong for me to choose his success over my love for him, or is his success just as or even more important?