My cat was diagnosed wth FIP, Feline Infection Perotinitis, a deadly disease with any cure for it.?

He always vomiting and suffering from diarrhea on a weekly basis. I feel so sorry for my cat. He's my baby, a great companion and I 'm devastated to see him suffering. How long is he going to live and be miserable? What should I do to him? I need a second opinion from anyone there.