What you may be missing here, is his possible sense of insecurity. Perhaps, he's been hurt before, even after a relationship got to the point where your Simself and he have gotten. So, the reaction was he was going to beat this new love to the punch. Since things obviously went wrong with a prior relationship, he's not going to be the one dumped.
Wouldn't have a thing to do with his feelings for his now wife. I think you should keep them together. They do have a child on the way, they both owe it to 'junior' to make it work.