Sorry you are here, but you've definitely come to the right place.
Read as much as you can on here. You'll see your story in the stories of so many others on here. The first thing you'll need to do is detach from your W. Your W is going through depression and grieving so you will need to be the one to be there for your children. As difficult as it may be, they'll need you to be the strong parent at this point.
Be thankful that your W is still cordial and wants to be friends. It's a start. Try to look at it this way - whether you end up D or back together, you'll need to start out by being friends first. Don't expect anything of her at this point.
You seem to be doing a good job of understanding her state of depression and not taking things personally. Work on yourself. Even though it wasn't your fault your wife had A, try to find out what was missing in your M that would make her try to find that missing element with someone else.
