Fat people need love, too. Just imagine how happy that guy is to have a guy that most people would say is too good for him. I know far too many unattractive and overweight gay guys that are so miserable you either have to put them on constant suicide watch, or you have to abandon them and be cold to their pain. Remember that feeling we get when we get a crush on a straight guy, how untouchable they are, how we could get so miserable because we could never have him? That's how they feel, all the time.
Besides, some guys, even reeeeally hot ones, just have a thing for smooshy soft skin. There are certainly weirder fetishes. Plus, the guy might be a total sweetheart, really loaded, really hung, or just really into the same things he is.