I've never done this before. I'd like to quit and not burn bridges. Any advise? We have no gigs booked, so it's not like I'm leaving Paul high and dry.
I have quit every band I've been in, apart from the current one, of course
I left my first regularly gigging band because I wanted to play a different style of music. The bassist was very pissed off. I remember being called a "psychopath" which I thought was rather over the top LOL. The others were more relaxed. The band broke up afterwards, which was a shame.
I quit another band because they planned to go touring and I didn't believe we had the organisational structure to make it viable (ie. pie-in-the-sky) and knew that if I quit work to tour I'd end up poor and struggle to find another job (unqualified). The main driver for touring, our singer, would always be fine because he was already on the dole and augmenting his income with black market activity.
Another time, some people in a fun band wanted to go serious and I didn't want to be serious about it. No bridges burnt, they understood.
I keep thinking of relationships. The basic principle, of course, is "It's not you, it's me"
Ideally, you'd tell them that you like them but you want to focus more on your main band. However, the "it's not you, it's me" might be hard to pull off given the recent friction, though.
I think the only way not to burn bridges would be to apologise to Paul for the harshness of the tone of your email to him, but even that might not guarantee good relations in the short to medium term. It might, however, open the door for good relations to resume after the dust settles. Thing is, no matter what your main reasons are, it would be hard for Paul and the others not to believe you're quitting due to his stage comments.
I guess sometimes we just gotta do what we gotta do, even if the odd bridge is burnt. It's not ideal, but what in life is?
Of course, there's also the option of trying to mend relationships and staying with them, which doesn't seem too rough, given that they don't gig a lot. Good luck either way!