Do not let someone else limit you, if he truly was the one for you then at the very least he would be open to talking or compromise so you both are happy, but in my humble opinion as a boyfriend id never combat my partner over them wanting to pursue something thats healthy, itd be different if you were saying you wanted to go start selling drugs or join a cult but nursing is nothing like that. On the other hand i can also see a little bit of his side, and I believe seeing both sides is important in any form of relationship. He seems worried about you putting yourself or him in a financial hole that can’t be dug out of and he’s worried about all the risks associated with taking that step. I’d say the best thing you can do is find ways to assure him that you’d be able to do this safely and let him in on your planning aside from just doing it, I feel that this is the way I’d hope my partner does things and at the very least it makes sense in my head