The band I'm setting up has come about precisely because the guitarist is in your situation. His long term band has been in a steady decline, members being replaced with less able and less interested people, gigs dropping off, no motivation. So he got chatting with me and we decided to set up something else with people who had the same ideas and goals as he has. He's keeping up his other band to keep his hand in but has rediscovered his mojo through this new project.
Perhaps you too could find another project to run in tandem so you don't have to leap into the abyss.
Good luck. I've been where you are and it's an awful place to be.