My pet rabbit just died today

Well I am very very upset right now. Two weeks ago I brought home a wonderful and sweet Mini-Rex Rabbit for my girlfriend. Even though I got him for her, he ended up becommming my rabbit. He was just the most awsome pet.. I don't know what happened.. He was fine.. then diareha.. then he just died. I took him to the vet as soon as I saw something wrong but I guess it was too late. Right now I feel so guilty.. I wasn't there when he died and he was alone, in a strange place surounded by strangers.