Can you give us a hint as to why you need to talk to him at all? Do you work with him? Do you have kids together?
Don’t give in to your temptation to tell him off. I’m guessing that he did something awful to you, but since you have already broken up, stay broken up. If you have to speak to him about something other than your relationship (still don’t quite understand why you have to see him or talk to him at all) then just be very business-like about the whole conversation.
Never allow yourself to become emotionally involved with him, when you are talking to him. Even if he asks you why you are “acting strange” or “being cold” which are huge buttons that men push when they want to drag you back into a situation that you have already exited. Just tell him that you two are no longer together and that all conversation will be 100% business-like and repeat it as often as you need to. If you slip up and start telling him how you really feel (angry, lovey-lovey, confused, disgusted, lustful) you will open up a big hole of vulnerability that he will drive a truck through.
He may deserve to be screamed at and told what a disgusting so and so he is, but if YOU are the one that does that, you will put yourself right back into the middle of the situation that you pulled yourself out of. Don’t allow that to happen. Hold your head up high, be business like with him, and move forward.