I went through the same thing you are going through now. It is heartbreaking, I know. So many people don't seem to "get" that, so I wanted to let you know that I DO. It was really hard for me to have my dx changed to Crohn's. For me, it was like being told I was sick all over again. So many people tried to reassure me, and tell me that it really wasn't any different than if I had UC, but the truth is that it is different. There are more complications, and you no longer have that "surgical cure".
I guess what I am trying to say is it's ok to be heartbroken for awhile. You kind of have to go through that whole greiving process all over again. At least I had to.