Gaining

I mean there's not really much you can do except give it time and see how he reacts in the future. I mean I suppose you could make some passing comment on your weight to prompt a certain response and gauge their reaction.

But ultimately being open and honest with one another is probably for the best. But apprehension when it comes to this fetish is understandable.

Is here looking at other heavier ladies, when
they pass by? This might indicate he likes them
and you.

There are ways to get his opinion without saying too much. You can say that your clothes are getting tight, and see if he comments.

If he comments on you being thick again, you could say something like "I know, right? But I kind of like it. I've got more curves, and I just feel like I have a little more presence than when I was so thin."

Which isn't telling him your fetish, but it tells him you like what has happened so far and are happy with your body, and that is a start of the conversation.

Basically, sometimes you just need to get a foot in the door, you don't have to smash the door into their face.

I think you should just be up front about it. You don't have to tell him it turns you on (though I think if you do and he is understanding it might bring you closer together) but you could simply say something like "hey I realize I've gained some weight weight and I'm wondering if it turns you off?" From there you can ask further questions. Like if he says he is into it you could ask him if he there would be point it would start bothering him and so on.