Definitely have to agree with NYS on his suggested read.
Speaking as a woman here, have you considered that perhaps since your wife did this in plain sight of you that she is reaching out to you in the only form of desperation that she knows will get your attention? I would say that she definitely got it finally...
I think regarding 180s that you need to look at your goals and what the 180s are...having her pay for half the expense sounds more controlling to me than a 180. How has your relationship been through the years...Who was the pursuer and who was the distancer...or were you both distancers? Her desire to be needed is human...and she was brave to tell you this...what can you do to make her feel needed? Sounds like your wife doesn't perhaps feel this right now...threatening to take her son away from her...as a mother that would cause me tremendous pain to have my child torn from me...just a mother's thoughts here.
Have you read Divorce Remedy yet? very good book and it may give you some insight as to the reason she did this...
