Gutwrenching-
Take my advice for what it's worth, b/c I have had no successes at the moment.... but I think you should do what Sandi suggested and tell her you will take the time between now and Christmas to decide. But I am putting a vote in for the kids on this one, if you can stomach having her in the house (b/c I know how hard this is). I say wait until after the holiday, otherwise your children will always associate Christmas with their mom leaving. I completely agree with setting boundaries and not condoning the affair, but i don't think a month would make that much of a difference one way or the other in making or breaking the marriage, and it would sure be good for the kids.