I left one band I set up after 18 months over 20 years ago. We were all in our early 20's playing original grunge-style rock. It started off as being great fun - we wrote loads of stuff really quickly and got loads of gigs and positive feedback. The rot started setting in as soon as the singer and drummer started making noises about 'making it'. We were in Cornwall playing a style of music that was a couple of years too late to be current. Yeah, really going to happen... Anyway, those two developed prima donna-ish attitudes, the singer started taking way too many drugs, the drummer retreated into self-indulgent angst, so I thought sod this, left, did an access course, then went to university. They carried on with another bassist, didn't write much more stuff and folded a year later.
No regrets.