Why didn't he talk to her before deciding to embark on an affair then, if communication is so important? He has still been sleeping with OP while sleeping with this other woman, pretending to be the family man, good dad and husband, it's not only the cheating to consider here, it is the year long deception, not to mention the risk to OP and his unborn child.
It' a bit one sided to say she should talk to him about it and forgive him, when he didn't bother to talk to her, people can be in happy relationships and have their head turned by someone else, it happens all the time in fact, people cheat, sometimes multiple times, but if you choose to cheat in the hope your wife/husband won't find out, there are no guarantees it will the way you want it to when they do find out.
All trust is gone and he doesn't deserve to ever have it back, I can't believe he would throw away his relationship and living with his children for a few shags on the side, I hope it was worth it to him to lose it all.