Gaining

It could be a fat fetish, or he might just find your belly sexy. It sounds like he enjoys your body either way though.

Have you tried bringing it up? From your previous posts it looks like you've been thinking about it for a while. If you chat to him about sex/bodies he might give you a few more clues..

Hopefully after dating him for 2.5 years, you can just come out and ask him. But if not, then make comments and see how he reacts. Tell him you want to be thin, and see what he says. Tell him if you eat any more you'll gain a lot of weight, and see what he says.