Divorce him,, right? I’m still in shock and don’t know what to do.
Well... on the upside, he's being honest and not lying/denying/gaslighting you, but I'm sure that doesn't feel like much of an upside right now.
He's completely changing the terms of your marriage, so no, you don't have to stay married if you don't married under these new terms, you don't have to.
So..... the first thing I would do if I were you is to set a deadline to make a decision. Give yourself either three or six months, and in the mean time, take care of yourself, get your ducks in a row, and find out your options.
It sounds like your husband wants to keep everything as is, but it's completely reasonable to ask him to start sleeping in another bedroom, or for your to, or if you don't have another bedroom, start sleeping on the couch.
Typically, people are advised to 180, which basically means detaching from the relationship and focusing on yourself, so no more doing his laundry, picking up his prescriptions at the pharmacy, calling and making appointments for him if he asked you to. He's a big boy and he can take care of all of his stuff now.
Find yourself a counselor. Preferably one that specializes in trauma or relationship issues. Figure out what YOU want. If you find yourself really struggling to get out of bed, eat, function normally, etc. consider starting antidepressants to get you through this for now.
DO NOT HAVE SEX WITH HIM. Even if he uses condoms with other women, some STDs can be transmitted anyways, like HPV.
Meet with a lawyer (or three) and find out your rights. Maybe today he's saying he wants an open marriage and tomorrow he's moving in with another woman. Who knows! But knowledge is power. Find out what your rights are, find out what you can expect if you should divorce.
Also look into legally separating. Not every state allows that, but you basically go over everything you would like in a divorce (Who pays the vet bill? Who pays for college? Who gets to declare the kids on their taxes? Sidenote: in my case, we each could declare one kid on our taxes, until our oldest was too old, and then we'd alternate years with our youngest.)
Talk to your doctor if you have trouble sleeping or losing weight. It's not unusual for someone to drop a lot of weight very quickly after news like this. Stay hydrated. If you have trouble eating, sip on protein shakes throughout the day.
Long story short, take care of yourself and your kids. Find out your options. Detach as much as you can so you can look at this situation (somewhat) objectively. You problem feel like you'll never be okay ever again, but with time and effort, you will be.