I want to be paid for helping my boyfriend sell his work
That seems reasonable. Why won't you pay you for your work now?
He has this opinion that I won't do it if he pays me.
It is wrong to ask people to work for free. You should not have to support a habit if you also have a job on the side.
I'm doing it for the world to be better and he should pay what I deserve anyway.
Even if you're doing something for a good cause doesn't mean you don't deserve to be paid. You put effort and skill into your trade and should be rewarded for it. You need to have a discussion with your boyfriend and figure something out so that this doesn't come in between your two's relationship.