I remember your case.
I don't think you've got anything to feel guilty for. I know me saying that won't make the guilt go away, but it really does seem like from an outsider's perspective that you have tried everything you humanly could. Perhaps in the future he will get the help he needs, but I don't think it's very likely and I wouldn't let it stop you from developing a new life in the meantime.
It's incredibly sad that all this seems to stem from a treatable physical illness, but it isn't you withholding the treatment. I guess I would try to view it the same way as I would an alcoholic or drug addict: you can see they're destroying their bodies and their lives, but you can't save them from themselves. Not if they are not interested in being saved.
Dx Crohn's in June 2000. (Yay )
Tried: 5-ASAs, azathioprine, 6MP, Remicade, methotrexate, Humira, diets.
1st surgery 20/2/13 - subtotal colectomy with end ileostomy.
2nd surgery 10/7/15 - ileorectal anastomosis. Stoma reversed and ileum connected to the rectum.
Current status: Chronic flare. Do I have any other kind?
Current meds: 50mg 6MP; Entyvio (started 3/11/16)