If your husband has never, ever acted inappropriately with other women in the past and he's now having an affair it could be related to some inner turmoil he feels about starting a family and being tied down, losing his freedom and youth, or an exacerbation of some undiagnosed mental health condition. It doesn't seem random that the timing of his affair is exactly the time when you're pregnant and having a child. There must be some connection.
In your case, if this has never happened before, your husband will most likely carry on with the affair until he and the OW have a fight and break up. At that point your husband might 'wake up' and realize he took all those risks for nothing and he'll come home ready to fix things. That's what happened with my husband - his affair ended and he came back. I was so angry, bitter, and resentful though and he didn't want to discuss what happened so it got worse and worse until he left again. If you want to save your marriage you need a lot of guidance at the point when he comes back to truly start the reconciliation process if he's willing to do the work.
It's very hard to forgive someone who goes and enjoys their time with another woman who most likely doesn't have a small child so she has all the time in the world to style her hair, do her makeup, and go on romantic dates while you're home in your pajamas looking like a mess struggling to care for a new baby. It's almost harder to forgive than it is to experience the loss you're feeling right now. The marriage is so broken and so much destruction has been done by the time the spouse comes back it's hard to even feel happy. Obviously though there are couples that successfully reconcile so you'll want to learn how that happens.
In the meantime, like right now, it's hard to let go especially when you let go and you see your loved one move on to someone else. If we lived in a society where families have influence over someone and intervene and if the affair becomes public around town then he'd probably come back. Sadly we live in a society and time in history when we value freedom and individuality and even the way marriage works in our culture makes it easy for someone to simply leave to pursue their own individual happiness. It's almost as if the system makes it too easy for affairs to happen and for someone to abandon their family.
I agree with how you're feeling about setting your husband free to enjoy his life with the other woman. It doesn't seem right. It's almost like you're enabling the affair by making it easier for him and all the conditions are now in place for him to move ahead full-steam. The problem is the only other thing you can do is file for divorce. If your husband is caught up in his affair he might agree to divorce because he's not willing to give up the other woman. The hope by not filing for divorce would be that your husband's affair will eventually end and he'll come back, ready to re-commit, without having to go through the pain and expense of divorce. I honestly think in theory promptly filing for divorce is the better option. It shows you're not willing to be a doormat and you have the strength to move on. The problem is we're so broken and unable to think or function in this state that being the one to file for divorce is almost impossible, not to mention you don't want to be the one to file when you're the one who wants to save the marriage.
It seems like a no-win situation. The only thing that helped in my case was when a friend starting calling me every day for several months and offered to fill the void that had been created by my husband leaving until I was strong enough to make it again. If you have a friend or family member who steps up and does that for you I bet you'll feel better. Counseling is great too but counselors only have an hour per week and it's hard to address everything in that one hour.
One other thing to mention if you're nursing an infant is that I believe cortisol and other hormones released by stress can be passed on to an infant and may or may not have a detrimental effect. Small babies can also sense good and bad things in their environments at basic levels so one incentive to try to re-gain your composure is to avoid any negative side effects you could be passing on to your baby. There are lot of things that happen within the first two years of a child's life that can affect them forever and right now your husband isn't there so you're left alone to create the most stable and loving environment possible for your baby. It's hard to do that alone so calling for help, having someone call you ever day or come to stay with you, might be the best thing you can do right now in this fragile state.
When my husband came back the first time I was so happy, happier than I've ever felt, that I completely forgot about DB and everything else. Everything was great for a while until it was clear my husband wasn't planning to make the effort to fix what he'd done. Just in case you leave this forum it's important to remember the marriage isn't yet fixed at the point when they come back. How you act at that time seems to correlate strongly with how likely the marriage is to succeed over the long term. You have to be strong and not let them back until they prove over an extended period of time that they're able to be trusted again. Even then it's never going to be the same.
The final advice I might offer right now is you have an opportunity to use the pain that you're feeling to help others. We tend to think inwardly when we're suffering and focus solely on eliminating our own suffering but you can help yourself and others by reaching out to people around you who in pain to encourage them. I bet others on this forum would appreciate hearing from you. There are lots of threads where no one gets a response because most others are only posting about themselves. If you see someone new and no one responded I bet they'd like to hear from you. Or if you have a neighbor who's sick or a friend struggling with a difficult pregnancy I bet they'd also appreciate your support.
There is still a strong chance your husband will be back so remembering this fact might help, at least temporarily, when you can barely function. We don't want to sit and wait for someone to come back. That's not what the DB approach suggests nor any other approach. You do have to take charge of your own life but if you look at the literature on affairs and infidelity it does appear that most affairs end and you will get a second chance at your marriage. It'd be great if you could keep us posted on the outcome.
