I know exactly what you are going through. My husband did the same thing, the affair. I know it's tempting to throw things back at him, especially when you see them together. But try not. Try not to talk to him at all. I wish I would've found this site sooner than I did, I really think I would be back with my husband sorting stuff out. The worst thing you can do after an affair is be very mean about it. I'm not saying you have no right to be mad or upset, but by acting a certain way shows a side of you your spouse has never seen before. Don't talk to him for a few days. You need to clear your mind. Think about you and your son. Because no matter what happens, your son will realize what your husband has done, and it will hurt him.
It's going to be a long road. It's been a month since I found out about my husbands affair, and I can't even think about it or I will go crazy. Take it one day at a time, and it's okay to cry. We're here for you.