So sorry the pain & heartbreak you have experienced. My WH cheated on me when we were married 13 years (seems to be the magic number.) I'm 6 months out from D Day, and I'm still hurting. There are better days, but it hasn't been easy.
My initial response was to throw him out, but his parents are 400 miles away and he is the sole provider. So didn't want to cut off my nose to spite my face. I'm glad I moved him into the guest bedroom instead. We have been through HELL, but it has been worth it. My FIRST advice to you is to tell your WH that there is to be NC! Period. If he breaks that, then you are out, dealbreaker. Even if you feel like D right now, you HAVE to give it at least 6 months before you make any major life decisions. There were times when I was DONE... would go weeks without talking to him, I've hit him (never have hit anybody in my life), but we have decided to make a new relationship. Our M wasn't good, I was extremely ill, and he felt sorry for himself. He always put himself first, thus why our marriage fell apart. Instead of being a man and leading this family into a healthier situation, he chose the cowards way out & sought out his first girlfriend.
Believe it or not, you're still in shock, this does get more painful as the realization this really happened. So, TAKE care of yourself! I lost 35 lbs. in 2 months, I couldn't eat. Start journaling (if you haven't started already.) This will help to verbalize your pain. If your WH really loves you & wants this to work, then he will do WHATEVER it takes to prove to you he is done with the OW & is committed to you.
How are your kids dealing with this? This is VERY traumatic for the kids. You should get all of you into counseling, beware, there are a lot of idiots out there. I've had horrible counselors and it's very disconcerting, but keep looking. Remember, we are always here if you need to vent.
Status: We're going to try IC one more time.
1) REMEMBER THIS IS NEVER YOUR FAULT. Although you may have contributed to the conditions that led to the affair. Having the affair is 100% your WH's fault, and only his.
2) I would expose to more people than just to your MIL. Tell his father, your parents, your older kids (in an age appropriate manner), to close friends that you both share, religious leader, etc. Expose all in ONE big swoop. Provide evidence if anyone asks. When exposing tell them that you need help in saving your marriage.
3) Confront: you have had what I would call a 'soft' confront. You need to outline the terms for him clearly on what he needs to do to save the marriage: initiate no contact via letter, STD check, write up a detailed timeline of the affair, copies of all cell phone records and credit card statements, turn over all passwords, social media accounts, no more guys nights out, no events involving alcohol unless you both are there, no texting or emailing other women except family, agreement to enter marital and individual counseling, change his phone #, etc. He is never to contact this prostitute again for the rest of his life.
4) If he doesn't agree to everything in #3 then tell him that you will be seeing a divorce attorney. The mere threat of a divorce will often shock waywards back into shape. Better yet if you can get papers drawn up and have him served, this most certainly will throw him for a loop. You can always withdraw the divorce motion later, but many times the shock of seeing what they will lose will often snap Waywards out of their fog.
Sending you strength and peace. No one should have to be in this position.