Stop letting him message you when he's drunk.
Stop letting him message you when he's high.
Stop letting him message you when he's lonely.
Stop letting him open your slowly healing wound.
Stop letting him back in.
Yes, I know you want to be there for him, as he's in pain too, but think on this, you've talked/messaged for hours and think maybe, just maybe this is his way of saying I do want to try and work this out, but I don't know how. You talk of old times, play familiar games of 'what's my favorite'?
You're worried about him. Is he taking care of himself? Is he eating right?
We're not talking about just a one-off message/talk session; we're talking about that this has been happening for days, or on and off for a while.
Then something happens that's important to you, NOT him, you!
You message him to tell him as he is your first thought of who you want to tell, and he makes it clear he really doesn't give a shit.
Sit up, take notice, and STOP!
STOP thinking about him and make yourself the priority.
Know your worth, which in case you're unsure, is f*cking priceless!