Brother, I feel your pain. My XWW cheated on and off for our entire relationship. Over 20 years. Just one guy (the Prick) but still. So, I get it.
Short answer, the pain will never fully go away.
It's kind of like losing a limb. You can recover and even be, in many ways, better...more fit, stronger & more social, etc...but it's always there.
We got divorced because I couldn't live with what she did, but we've been seeing each other as a couple for several years now. Things are, in many ways, better. We're closer, more communicative and honest about feelings with each other. I am a better person, too. Fit, strong, more social and assertive, etc.
A lot of the fear/doubt is gone, but it's still there. We have 4 kids who, along with many family and friends, ask 'why don't you guys get married?'. She's asked it and so have I, to myself. Why not?
Because it's still there.
Like you I suffer from low self esteem, because of my life-long weight problem. Even though I've lost, like eighty lbs of fat, put on considerable muscle and get a lot of attention from other women, my issues haunt me.
She was my 'dream girl', way out of my league in my mind and I was lucky to have her. She's a 'girl next door' shy, demure, very conservative type who dresses in long skirts, high-cut blouses, horn-rimmed glasses (yep, they still make those) and to look at her you'd never have expected this. She looks like Dawn Wells' stunt double. Really. Very pretty, but she has/had low self-esteem too.
When it all came out, I and much of my world view was shattered. It was only through a lot of therapy and a surprising amount of work and understanding from XWW that I was able to pull out of it.
So, enough preliminary stuff. Didn't mean to thread-jack.
So I ask you to ask yourself, what have YOU done to improve things, for yourself? Therapy? The gym? Hobbies? Honest discussion?
What has your WIFE done to improve things, for you and the relationship? Therapy? Honesty? Transparency? Patient understanding?
Those things are foundational, IMHO. Also, I'm not fully aware of everything in your story. So, how did you find out? Did she confess? Was she outed or did you discover? It matters. In order to move forward many of us BS must know details. What has she shared, or been willing to share, about the length, frequency and intensity of he extra-marital relationships?
I get it if you don't want to know everything. I had the misfortune of seeing videos of her with AP that he secretly recorded and she was very different than what I was used to.
Precise details may not be easy for you to hear or for her to tell, but if you need them, then you need them. Be honest with her and yourself.
Marriage couseling in the early stages is usually a mistake. It takes someone (a counselor) who specializes in adultery to help you navigate though all the emotions, etc. Usually it's best for you each to do individual couseling. Have you each done it? You, for the trauma this has inflicted upon you, and yes it is a trauma as real and devastating as a car wreck or an assault. Her, to figure out why she did this, why she allowed herself to do this and to cope with her guilt (which I hope she has, as it's a good sign of remorse) for the pain and damage caused to you, HER and the relationship. Also on how to make herself a 'safe' partner for your marriage. You have to feel confident this won't happen again.
As others have said, the issues won't go away by themselves. They have to be addressed head on, with or without outside help. If not they'll only fester and build a resentment that will metastasize into all other areas of your lives. Especially devastating with a new baby coming.
Your old relationship is possibly over and, if so, should be mourned, as XWW and I mourned ours. But maybe you can build a new and possibly better relationship, diffrent in some ways, but possibly better. Hard work. Very hard work, but possible.
Whatever the future holds, I think it's safe enough to say that I and others in this community are rooting for you. You WILL be fine!