Welcome to the best club no one ever wanted to join. Happy that you were able to find us, sorry that you had the need.
Immediately, how are the kids? How heartless to do that in front of the child that I'm sure you've raised as your own for the last decade our so. How is he? I can't help but feel his devastation as well as your own. WTF?
First, lets help you so that you can help the kids. In the upper left corner is something called the healing library. You need to read it all, but for now, please focus on BS FAQ #11 and implement it. When/if she gets home, please, please do NOT discuss things with her other than the kids and finances.
Second, you need to set up some appointments. Primarily, a lawyer. Not necessarily to begun divorce proceedings, but to see what your rights and responsibilities are. If divorce becomes inevitable, do not assume that she will automatically get custody. My ex WW(wandering wife) did and she was wrong. Paid me CS for 15 years. The court thought I would make the better parent in spite of the fact there was a half sibling involved.
Third, line up a doctor for STD testing. Unfortunately there is a high percentage of people who are infected with something in this day and age. Your WW probably isn't this guys first conquest. You need to protect yourself. Condoms are NOT effective against all STD's. HPV comes to mind first.
Fourth, watch your health. Make sure you are eating and drinking enough. You're kids will need you at your best to help them through this terrible time. If sleep becomes an issue, or anxiety, please talk to your dr about those as well.
Do you know who the AP(affair partner) is? Please notify their BSO(betrayed significant other) of the ongoing affair. Wouldn't you want someone to tell you? Also, affairs cannot survive the light of day. Get this BS(ya, that one) out in the open. So not tell your SO you are doing this. That is crucial.
Fifth and final. This is a great place to learn. Sometimes the advice doesn't seen to sit right, but there are a lot of people here who have BTDT. The advice is hard earned but generally very accurate.
Again, sorry that you are here. So glad you made it.
Eta auto correct sucks