as a person who likes cats, i want to send you my sympathies. it's a terrible thing to find thigs out and i would have a terrible time deciding what to do.
i had to put my dog wolfie to sleep about 4 years ago now. i was absolutely strong till he sighed out that last breath, then i burst into tears....as did the vet and the vet tech along with me. its the hardest and most loving thing a pet owner can do for their furrbabies.