I would second everything that everyone has said re thr pregnancy bringing up his emotions about losing the baby.

I also thought I'd throw in there about the IVF conception. It's a very clinical way to go about it, so he could feel dissociated from the whole conception thing too because all he had to do was "shake in a cup" so to speak. It's certainly not the intimate and enjoyable process that we are all lead to believe it will be, so maybe that's brought up some strange feelings for him too?

But mostly, I'd say he's probably processing the loss from his previous relationship and maybe you could try talking to him about that?