I'm not going to boo and hiss at you, H, but I wish i could give you a good shake - in a well-meant manner!
The guy may be charming and wonderful, but he's a rat. Sometimes they lie about their wives being pregnant, to get out of a relationship that's run its course. He's had his fun, and now it's time to go, sort of thing.
If the wife really is pregnant, then you can see what sort of guy you've found yourself, and he could just as easily do it you or someone else.
Pregnant women often get tetchy, or go off sex, but a decent guy wouldn't dream of having an extra-marital affair just because of that. He'd be there supporting his wife. Hun - get "Gloria" on, and put him down to good riddance to bad rubbish, even though you're hurting right now. x