Though I do agree with you on some part, it WOULD be better for him to tell her personally, rather then, say, a clever bad guy blurting it out and making it sound like he’s only into her for the fetish.
In other words, I don’t think he should wait till after the pregnancy is over, especially sense who knows how long that will take.

It ought to be similar to being fascinated with any other physical attribute of your girlfriend/boyfriend. There’s a time to share and there’s a time when it’s too soon.

If he felt this way about Cait before the whole pregnancy thing, then telling her would only serve to cast doubt in her eyes as to how true his feelings for her really are.

Not telling her doesn’t mean he’s lying to her, or withholding any evidence. It’s just something that wouldn’t really help matters any if the secret got out.

I think the best time to mention it would be later, after the god-borne pregnancy is gone. Maybe when the two of them are ready to have children on their own, even.