I had several of these "talks" with my H when he was in A. It was excruiating for me but it was important that he see me as listening to his side.
Here are the important things for you: Maintain neutral facial expressions. Some of what he is going to say will be untrue and cruel but DO NOT REACT! He'll be trying to bait you into an argument so he can be right about his version of your history.
Just listen. When appropriate say things like..."I'm sorry you've felt this way" "I hear what you're saying" Dr Phil's Relationship Rescue has some really good validation statements.
Don't let him lie. If he lies, call him on it and refuse to go any further if he is unwilling to acknowledge the truth. Puppy had a good response for lies.
And cut yourself some slack. This is not going to be easy but it's a necessary step. It will take some practice not to get drawn into a fight. If you feel it happening, just say that you need a break, get a drink of water, have to go to the bathroom, anything to give yourself a minute to pull it together.
