Find a simple, self-respecting way to tell her the primary reason (don't make yourself look weak, just have respect for yourself). Don't be wordy - less is more. I think it goes without saying that you should not mention the 2nd reason.
25 gave me this... "Right now I need to reduce contact with you, so I can move forward"
Me: 44 W: 45 S: 11 Married: 15 Together: 18 BD: 9/29/2014 OM discovered: 10/16/2014 I left her behind: 12/14/2014