It sounds like she's communicating calmly and respectfully and that she's really not happy. I don't see any attempts on her part to shame you or to cause you feel guilt. It's also reasonable that she's done some research as to her options. I second the advice not to move out - it's not okay she's consulting your kids about this, but you can't do anything about that. If she wants to separate, she can and should do the moving out and the leg work of arranging it all.
I think the best thing to do is give her as much space as you can. You can stop doing husbandly-type things for her, given that she doesn't want to be your wife - and you can do that peacefully. She may well be in an affair, but it really isn't a given. I BD'd my husband and there was no-one else for me - I just didn't want the marriage any longer as it stood. Yes, watch her behaviour - but be careful your assumptions don't make her into an enemy when the facts might be simpler - she's unhappy and is trying to make herself happy.
