General

I think the key is not starting with "I have a fat fetish"

Tell him how attractive you find him, his body, everything, the same way you would tell anyone, don't focus on the fat, but don't avoid it either, it is part of who he is and you love all of him.

Once you can get him comfortable with the idea of you finding him attractive fat, then you can worry about the rest of it.

I have been in your shoes. You never quite know exactly how people are going to react. How did I handle it? First of all i made sure he knew just how much I enjoyed his extra wieght. I did things like when we sat next to each other i would gently stroke the tum not in an overt way but in a I really like the way this feels and I am going to make sure you like it too. Secondly I finally just had to come out with it. Told him straight up this is how I feel about your body now and it makes me so happy and it turns me on completly. Most of the time with guys if you tell them you like it they will be ok with what ever your trip is. If he is not comfy with it you may just have to deal with that reality as well but seriously if you love each other then you should be comfy enough to just say hey i like this very very much can we keep it??

Eh, just do what I did...

Forget to close the web browser after being on FF...lol