You have a RIGHT to know. It is ok and the right thing to do. The TRUTH of what is going on is a must. Yes, it hurts to the core and I understand that.
I know you are supposed to meet tomorrow. The problem is that this is so fresh in your mind that it will be very very difficult for you to not make numerous mistakes at the meeting.
One of the things that I have seen work to end affairs in the past is for the betrayed spouse to expose the affair. By exposing, I mean exposing it to HIS wife. He is more than likely lying to his wife AND to your wife. He may be telling your wife he is leaving his wife. That is normal for a married man to tell his affair partner. Your wife probably believes that. If you expose it to his wife you could blow this affair out of the water. If he is lying to your wife, and his wife finds out, he may very well drop your wife like a hot potato. She would then probably give your relationship another chance. I have seen that happen many times. I think it is worth the risk. If he is going to leave his wife, then you have lost nothing anyway right?