Welcome to SI, the home of the greatest group of people that you never wanted to meet.
Also, some folks might come to your thread and tell you that you must do this or that. You don't have to, you do you (with helpful advice). You know those folks that call out at the theater, "Don't go up those stairs!" or "Don't go down in the basement!"? Well, some here are doing that, they're hurt and trying to tell you to do what they thought that they should have done. An SI motto is, "Take what you need and leave the rest." Do _that_.
You're riding The Emotional Rollercoaster, where your emotions change on a dime and whip you right and left. Keep your hands, feet, and head inside the car at all times. It will get better. It can take a while, no fooling, but it _does_ get better.
The reason that you're feeling like this is that he's broken your "personal narrative," which is our internal story of how we got where we are in life, our basic beliefs, etc. Your narrative was, "I'm married. My husband loves me. He wouldn't cheat on me." He broke that trust.
By lying to you and cheating on you he also took your "personal agency", which is the ability to make fully informed decisions about your life. _He_ was making the decisions, and he didn't include you.
Do not accept the following from him:
Blameshifting - where he might try to blame you or the marriage for his cheating. That's frankly bullshit. You were in the same marriage and you did not cheat.
Rugsweeping - "Baby, if we just forget all this and put it behind us then everything will be better." It won't. Things swept under the rug grow big fangs and sharp claws and come out all mad and stuff years later. Rugswept things fester and grow and foster resentment.
Minimizing - "This was a mistake!" It wasn't a mistake. A mistake is when I picked up chocolate milk at the store instead of whole milk. An A(ffair) is a series of _choices_. Each decision to talk to his A(ffair)P(artner) was a _choice_. A choice that you were not part of.
On this site, in the upper left, is a link to The Healing Library. Under there is a BS FAQ. Item #11 is "The 180." The 180 is a tool for you to help detach from the madness. You should use it.
He created this mess and he has an awful lot of work ahead of him to 1) feel remorse at what he's done, and 2) fix his entitled mentality. You see, he could have come to you and said, "We need M(arriage)C(ounseling)." Or he could have said, "We need to D(ivorce).", or any number of things. He didn't do any of that, however, he _chose_ to cheat. He needs help, an I(ndividual)C(ounselor) to help him figure out his "Why-s".
If he tries, "Baby, you ignored me!" your answer, if you give one, should be "Why does that make it ok for you to lie and cheat?" If he tries, "I was angry", same answer. His Why-s are likely rooted deep in his FOO (Family Of Origin) issues. it takes IC to help dig into that.
Don't make the mistake of MC before IC, because MC assumes that _both_ of you are being truthful and willing to work on the M, and right now he isn't being truthful.
Be aware of the difference between Regret and Remorse. Regret is crying (crocodile tears) because he's sorry he got caught. Remorse is empathy, knowing how badly he hurt you and feeling terrible for _you_.
Others will be along shortly and offer you more help. You might keep your replies in this thread for a while, though you certainly don't have to. Keeping things here for a bit helps SI folks find your story in your first post and then jump to the end of the thread to see where you are right now. It also makes it easier for you to find your most recent Q's and A's.
Nice to meet you, sorry that you had to find us, and a fist-bump, sister in adversity. }{