No one wants to be here. No one wants to experience this, and for that I'm truly sorry he's putting you through this.
Make no mistake HE is the one that is hurting you with his actions. You are especially vunerable right now, as a mother. The way you feel right now is your "wife" feelings that have been damaged beyond imagination. Your self esteem, trust and your entire life feel like they are in the balance of the decisions weighing on you, on top of baking a human being inside you. This is a lot to process and unpack all at once.
You need to be able to clear the air with his parents. You don't need them to pick sides, but you don't need to protect your WS for their sake. He made this mess, let him sit in the uncomfortable part of it that is accountability.
Only you can decide if you believe he is sorry, will change, or that your marriage is worth the risk. Know without a doubt that many have traveled this path and for many it's the first of a long line of future affairs. If you asked those people if they thought they could save their marriage when it happened, and that their marriage survived, it would be both ends of the spectrum.
Some have affairs once, marriages survive though intensive work, building trust and days, weeks, months or years of hard work and do eventually thrive again, but the damage is always in the background. An arguement or hurt brings that to the surface so it's never really gone.
Unfortunately a large amount of us here, end up here more than once. Our WS does it again, whether it's 2 times, or dozens of times. Often we don't put it together for years, and then it blindsides us again. By that time we've wasted precious years believing in a fantasy that they'd never hurt us again.
Right now your priority needs to be yourself, baby, toddler and not ruminating and being in constant fear of the future. Take all the time you need. This is important that you remember who is important in this situation. The lessons you learn now will impact your new baby and your toddler, so weigh out your future life if you stay.
Will he be the father that your children need? Will he be someone you and they are proud of. Will he take full accountability for his actions and do everything necessary to have a healthy relationship, or will he try to sweep this under the rug and let you suffer through it? All important things to consider. How he acts now in this uncomfortable space will give you answers.
His only concern right now should be you and your children. You did nothing wrong. You aren't worthless. Nothing you did could cause him to do what he did. Don't give him that power in your head. Infidelity has ZERO to do with the victim, and 100% to do with the one cheating. It speaks volumes as to how they respect their spouse and themselves. They risk it all for some instant ego boost and validation.
They aren't sorry when it's happening, but they are when they get caught. That isn't accountability, that's victim shaming and flipping the script. They often leave out details, don't fully confess, and continue to skirt the truth. Until you know the full truth, absolute transparancy you can't weigh your options and make any informed decisions. The only way to the other side is through every bit of the hurt. I highy recommend counciling. It will help give you healthy ways to process when you want to shut down completely. Couples counciling is best but often they won't go.
Right now you're filled with pregnancy hormones, have a toddler and your WS is not really suffering. He's at his parents, and probably sold them a half truth story, because he knows what he did. I can't tell you what path is best for you, but choose wisely. No one wants to be on this forum a second time, wishing they'd made different choices.