Put together an thoughtful letter that goes something like:
I am sorry to tell you that our marriage is in trouble. _____ has been having an affair with a 23 year old man with a troubled history, and I have asked her to leave, not because I do not want to fight for my marriage, but because I want to protect myself and our children from this predator she is seeing and because her behavior is not something I want our children to be continually exposed to.
I appreciate your support in this matter.
Give them each copies of the letter. Then step back. She is going to get angry because you didn't help her carry out her Big Lie. She is going to run "damage control" and spin many more webs of deceit. Do not engage her. If you say anything, ask her if she has found an apartment yet or say you did not want to lie for her.
It's the right thing to do.
"What is best for my kids is best for me"
Persevere = happily being patient over a long period of time