Addressing my father's infidelity

Hello,
I am new to this site. I found out 2 days ago that my father has been cheating on my mother for a few months. My mother was obviously distraught, but she has decided to work on the marriage. I have a number of things I want to say to my father, but I'm wondering what the best approach would be. Should I email him or address things in person? I am visiting in a couple weeks. I was considering email because I feel that I can best express myself in that way and I'd like my dad to remember what I tell him.

Also, I'm wondering about the content of my message. A part of me wants to really let him have it and another part knows that he is hurting right now as well. Some advice would be greatly appreciated!

I think your father's sex life is none of your business. Why would he be interested in your opinion? Do you really think what you say will be news to him? I'm sorry if your mother is confiding in you. She really should leave you out of it. This is between them, especially if you are no longer living at home. Trust me, you don't want to hear details, and you don't want to get stuck with either one of them. You have your own life to look after.

The only possible reason I see - one that would justify an email or a conversation - is to let him know that you know, so that there is clarity because otherwise he and you might feel awkward around each other. Such an email or a conversation should be completely non-judgmental (meaning - COMPLETELY, in both directions - either accusations or expressions of support are out of place) and simply factual.