FrankieB, I've never performed with my SO because he just doesn't do music, except as an avid listener. I grew up singing with my parents and sisters and, sometimes my brother. At those times, I think, because we learned it from birth, there was never a problem about getting along.
Over the past 20 odd years, though, I've also promoted and performed with my brother, who is a classical composer (tempermental, too!) It has not been easy. There is a lot of ego involved, both for him as the composer and me, as the performer and person who knows a lot more about marketing than he ever will!
For us, it came down to our love of the music itself being the most important thing. Second it was that I deferred to him, as it was his original music; only he, at the time, knew the way it was supposed to sound and I had to work with that.
We worked with two other singers, at different times, which wound up being really interesting. One was professionally trained and made her living giving voice lessons and performing. She felt the same way I did about the music and followed the composer's lead.
The other singer was mostly self-taught like me, only she'd been in choruses and had some formal training in school, while I'd been in orchestra and not trained my voice as much. When we were rehearsing she kept getting a certain song's phrasing wrong. My brother was trying to be very diplomatic about it. I finally lost my temper and told her off, stomped off of the stage and sat down in one of the seats. After some coaxing form my brother, she and I talked it out. She finally understood the phrasing and we got it right. She and I had been best friends before that. After, we grew even closer and attributed some of that to our "having it out."
My SO sometimes knows everything!**BG** So, we get into it. We usually agree to disagree and end up assuring one another that we know more than the other. This is not just about music, but many things in general. We are both strong personalities and knowledgable in some things, so...we have opinions!
The best advice I could say from those various experiences is the love of the music making the difference. What is it that sets you two off? The interpretation? Who does harmony and does lead? If you can share a bit more with us, I'll bet there are others here who will be of more help than me. You've posed an interesting question, I think, one worthy of more discussion. Thanks,