I hate fistulas!
I had at least of three of them (I was up to 3 setons at one point). The first one showed up in 2001. Finally in 2010 I started Remicade and that did help initially to close the holes. I was told I have complex fistulas (the really bad ones). In April I had to go to perm. ileo. because my fistulas and cuff were too horrible and my GI was very concerned (even mentioning the risk of cancer in the fistula tracks). The fistulas are what changed my diagnosis to Crohn's.
Keep up the bulking foods! I also did lots of sitz baths to keep everything very clean. I really didn't want to the perm. ileo. , but I'm so glad to be able to swim this year and not have to worry about wearing a maxi pad to catch all the fistula drainage and stay on the side of the pool. I hope yours never progress to the point of mine.