Your situation is a classic example of what can happen entering into collaborative effort without having a written agreement on control and or ownership of your intellectual work.
Truly this sucks and I feel bad for you. Before I’d play another note with this guy, he needs to understand that you own your work. Secondly, you have no intentions of playing his crap parts, and if he ever decides to publish this work (which is a really good idea if you plan on having your stuff on the internet) without your bass parts he better disclose you are not the bassist.
I hope you can get this straightened out.