I completely understand how these things can be normalised over time and that must be a real headfuck.
From the outside though, having a dad who disappears randomly for 100 nights over a couple of years and then trundles back in to sleep on the sofa... is really fucking confusing and is showing them that it's a woman's job to 'run' a family and a man's right to have the freedom to be entirely selfish and dip in and out of family life as he chooses.
This is so very damaging to them. You've had the divorce papers ready for a couple of months. It really is time now.
The longer you stay, the more likely it is your children will replicate this relationship dynamic as adults.
Either taking on your role (being treated like shit) or, taking on his role - being selfish pricks who treat women appallingly and disrespectfully.
Both would break your heart, surely?
You need to stop worrying about his reaction and get the divorce signed.
He's not exactly got much get up and go has he? It doesn't sound like he's going to be threatening or dangerous when you file.
He'll pop on the dressing gown of doom, do sad eyes, at some point threaten to harm himself saying he's nothing to live for, try and guilt you saying he has nowhere to go, say you're cold and never cared about him, how could you do this etc. But he's a grown man.
And if he can afford all that travel and gig tickets, he'll just have to now use it for any costs associated with the break up like a big boy.