Gaining

If you understand her fantasies better, might be able to do some play with them, without really gaining. Like having an evening where you pad your clothes to look fatter, and play the part of her fat pig. Or occasionally going to a buffet and really overdoing it ( and talking it up), or letting her hand feed you.

Just something to think about. Think of it as (fat) porn for her, turning her crank via fantasy.

You could always gain a few pounds, like 10-15 and if you like it. If not, it's not the end of the world and you easily lose it ...

I have the same issues a lot most guys I have met over the years weren't into it either darn it I seem to be cursed