mutatio, it was a tough thing she did and the others have guided you really well in your future action.
A man admits his oversight to another man (your S) and asks him how he feels about it and that you won't let it happen again. That kind of conversation is worth so much more than some ink on a piece of decorated cardboard. Also it shows that you take the morale high ground and not try to show your W up in front of the family.
Who's the better parent now then?
As far as your relationship with your W is concerned, ignore it as the others have said, let it go and show her you've moved on by not letting her silly games affect your way of thinking or feelings.
- Nobody has ever learnt anything important from happiness and success; problems make us grow - Consult your plan, not your feelings - If you haven't set goals, how can you expect to achieve anything?