Credence has such a kindness/praise kink that, while he can control himself in public, as soon as he's alone and recalling whomever was nice to him he has a raging boner. Of course he's ashamed of it because he's taking something perfectly innocent and making it sexual but he can't help it. Still gets off on it though.

And it happens with everyone.

Grindlegraves touches him sweetly and says nice things about him? Boner.

Jacob feeds him and smiles at him? boner.

Etc Etc.

Please no underage or incest (and yes I mean Mrs. Barebone, Charity and Modesty even though they're all adopted)