Hi bmb12, Welcome to Healing Well.
I agree with what has been said. He definitely needs to get in to see a GI asap. It sounds like he has really bad inflammation in the rectum if it hurts to insert the tip of the enema. He may do better with a hydrocortisone enema, he may also have something else going on that is causing some extra pain, like a fissure. Those can also be helped by cortifoam or suppositories.
It sounds like you're very supportive of him and that is truly wonderful. I don't think there is anything more important than being there for him and being understanding of his condition. As for diet, I think avoiding artificial sweetners helps the majority of us. Is he taking vitamins? Most UCers are deficient in vitamin D, it would probably be good to get him started on a supplement.
It's too bad he can't get into the new GI for 2 weeks. Perhaps you could call and get him on the cancellation list? He may need a course of prednisone or maybe he could change to a different mesalamine medication is Asacol is no longer helping him.. I was in the same boat, Asacol stopped managing my UC. I tried to calm things with prednisone but I couldn't taper off without having symptoms return. After much denial, I started 6mp and I have been feeling better since. I still have ups and down (bad days and good days) but so far, the downs have been manageable.
Another thing, if he is stressed, he may benefit from speaking with someone and possibly treating the anxiety and stress.