First of all, you're so close to DDay, you have little to no control over your emotions, only your actions.
There's not a lot on your backstory to go by, but here's my take;
1) Your kids are a pretty good age. In fact, one of her A's was with your child's friend's parent. They may be keenly aware of the A.
2) Without getting into details with them, I would say something along the lines that "Mom and Dad aren't getting along right now. We are both here for you, but not for each other".
3) You can be a bit sympathetic without being emotionally involved. I personally think it's good to display sympathy.
4) I wouldn't let yourself be a sounding board, just to offer to help if she really needs it.
5) No guilt in being emotionally removed. She's the one who caused it, not you.
Whenever there's children involved, you need to be somewhat sensitive. They can't be used for emotional blackmail by either parent, but at the same time, the kids deserve to have both parents treated with respect in front of them.
My WW is also a hypochondriac. But even before the A, I tuned it out. In the cases where it became something more, I showed true empathy.
6 Do not be anxious about anything, but in every situation, by prayer and petition, with thanksgiving, present your requests to God. 7 And the peace of God, which transcends all understanding, will guard your hearts and your mind