I really feel like a girlfriend just left me

With all due respect and understanding, this is the wrong attitude, and can lead to worsening the situation for yourself and potentially others too. You should think of it more like a job. Be professional. Remember that you are still qualified and there are lots of other opportunities. Don't show up to your bandmates house at 3am in tears. Don't bombard them with messages begging them to take you back. Don't pull any guilt trip stuff (this includes getting super wasted all the time btw). I've been on both sides of this situation and I'm speaking from experience here. This might sound like an obvious thing to say, but you'd be surprised how many grown adults do this kind of thing.