I'm having a hard time understanding your situation. I myself am a codie, enabler whatever you want to call us, but really, you have endured way more than your obligation to him.
you know why he's always in pain, because he's using an opiate to feel better. Opiates will make you feel like crap when not enough is in your system. I hear ya about his skin graphs and surgeries but why do you think the doctors won't give him pain killers? Because they see whats going on thats why.
I'm saying all of this with nothing but love and support ..... do you need a kick in the pants to see what you need? It will be hard but trust me after you leave or kick him out or whatever you do to be rid of him you will let out a big sigh of relief and start really living again.
Noone and I mean noone should put up with this. The things he says or does is only to keep you doing what your doing. You are no different than any of us who have been codies/enablers so when we say things to you it's from experience not just smoke up your butt.
I tell you what, give it a trial run, go away for a long weekend, even if its to a friends or family member. Don't tell him where your going just say your going on a mini vacation because you need it. And you really have to stop the what if's.
good luck