She''s thrown her nine year old out of the house

I think the best thing you can do is to provide emotional support and a listening ear for your partner. While I can understand why you feel that what has happened is wrong, when a third party is mixed into an already conflicted situation, it only makes matters worse. Your own opinion of your partner''s ex may be clouding your over-view of the actual situation somewhat.

If you do want to give your partner some advice, then the best advice you can give him, is to join Wikivorce himself, and we can offer information/advice/support directly