So sorry.
I am currently going through similar, though can't quite say I've survived yet
I have a DD with my partner, and found out I was expecting our (planned) DC2 back in May. A couple of weeks later I found out he has been having a year long affair with a 17yo (he is 45btw)
I also had no idea, and have very mixed emotions about it - anger, disgust, loss, worry for my childrens future, annoyance with myself for not realising, etc.
I am surviving day to day for the sake of my DD and bump. Ultimately, I know deep down that we'll be happier without someone in our lives that can treat us in this way.
Do you have friends/family that you can confide in? If everyone thinks you're doing okay, you perhaps aren't getting the support that you so desparately need.
I am so grateful that I wailed to all of my fam and friends, they've each been very helpful and supportive in their own ways.