This thread is very interesting. I would love an opportunity to show some backbone to my wife, but I'm not sure how to apply any boundaries in my sitch.
My W has shown no concern for our M. She has stated, flat out, that her A (which she calls a R) makes her happy, and I don't. Given a choice, right now, she would choose him without blinking an eye. Our C only regards S3, no R or M talks, not even small talk. We work well, mostly, regarding timesharing.
I don't really see how I can use boundaries to directly impact my M, when she does not care about it. I can't force her to reconsider how she feels about me. I can only imagine boundaries involving our S, but I have relatively few complaints about how we work together for him.
There is one thing. I would like her to be transparent about her activities w/ him. Mainly to be sure she's not doing anything messed up with OM in front of our S. I suppose a custody petition could be an enforcement. Might there be other possible enforcements?
