"Don't quit your job until you have another lined up."
OP hasn't indicated that he relies on the band for income, so the only thing he seems to be getting out of it in an ongoing capacity is headaches and time wasted. OP is already in 3 bands, which is a lot. There is also a possibility of either kicking the guitarist (considering he is clearly the "problem member") or starting a new band with the drummer. Being in a band Even if he didn't have all of that, it's not as if he can't continue to be musically productive in the interim (e.g. focusing on writing material he can bring to bands he might form/join in the future).
"Don't make any major decisions when you're angry, hungry or tired."
It's probably been long enough such that it won't be an emotional decision. And even if it's a decision made in a high-stress situation, this is probably unavoidable because the guitarists outbursts seem to be an ongoing thing. If it's an angry decision now, it will likely be an angry decision a month from now as the guitarist will likely continue to throw tantrums and treat people like crap.
"Lastly, drunk guy is simply projecting on to you what he hates most about himself, inability to stop."
Perhaps. And OP should take that into account and not look down on the dude (and probably already does considering he used to have drinking problems). However, recognizing this doesn't make the guitarist's behavior any less tolerable or damaging to OP's well-being. The same sorta excuses are frequently used to justify staying in an abusive relationship. You're not wrong, but OP shouldn't stick around and take that poopie if it's going to continue. Show understanding, sure. But don't tolerate it on an ongoing basis. From what we know (which, albeit, isn't all that much in the grand scheme of things), it sounds like it will continue to happen.