I don't have any experience with what you're going through now so all I can offer is support. The thought that has helped me often through illness, surgeries, jpouch adaption, semi-incontinence and therapy, is that there will come a point in a foreseeable amount of time when the hardship will have become part of the past. Which doesn't necessarily answer your questions right now. We come to the ends of certain limits and think we can't possibly go on, but we find ways to go on.
Based on what you are saying about your doctor, it might be the time to get other opinions. Spend some time researching the right one/s and don't be afraid to do a little traveling to see them. Another doctor could have a different take on your fistula situation and change the course of things somewhat, for healing and for a way that makes your life more comfortable.
Hang in there.
UC Dx and then 7 years of no symtoms. But when they started, they didn't let up, ASA stopped working, pred stopped working, and azathioprin did nothing. The threat of much more radical drugs, plus the fact that a stricture was about to shut down my colon, led to my decision for a total colectomy in April 2011, 2nd step December 2011 and ... TAKE-DOWN WAS ON MARCH 19, 2012.