I think an underrated aspect of this whole thing is how the "partner" is apparently treating OP. I agree with all the comments so far about lessons, and studying notes/theory, and all that basic "learning an instrument" stuff. However, if your primary playing partner is seemingly compounding the issue of your inability to play bass whatsoever, I'd have a serious think-session about the end goal of this project and what you are getting out of it. Then have a discussion with Partner about your frustrations and try to constructively share your thoughts on how you feel unable to keep up and that you may need to work a little on your personal skill level before diving back into writing bass parts for original music.
Also keep in mind that I am pretty sure most of us on here didn't first learn the bass guitar by writing for new, original material before even having a handle on our respective playing abilities. I taught myself bass by reading tips on how to correctly place my hands on the frets/strings and then learning as many songs on bass as I could. I created an iTunes playlist of about 50 songs and then spent my free time learning and playing along with each one. This also eventually taught me how to dial in tones as I tried to match the recordings after awhile.
We are all here to help you get to where you want to go with your bass guitar.
Cheers
Also keep in mind that I am pretty sure most of us on here didn't first learn the bass guitar by writing for new, original material before even having a handle on our respective playing abilities. I taught myself bass by reading tips on how to correctly place my hands on the frets/strings and then learning as many songs on bass as I could. I created an iTunes playlist of about 50 songs and then spent my free time learning and playing along with each one. This also eventually taught me how to dial in tones as I tried to match the recordings after awhile.
We are all here to help you get to where you want to go with your bass guitar.
Cheers