My current question for myself is do I state that boundary directly now, or trust that she understands my boundary already and simply take action when/if it is crossed?  In a healthy relationship, I think an extra marital affair is a boundary that does not have to be stated.

If you give in here and she pursues her desires, what happens when that relationship is not enough?  Where's the limit?  Three partners?  Five?  Ten?

Pete -  we did discuss this a little last night - that an extramarital relationship not only involves her, but also me and the kids.  The desire to have another long term partner is completely different than the desire for sexual curiosity and pleasure.  The latter creates unstable situations for me and the kids and is purely selfish.  That’s why I asked her point blank if she viewed this other woman as another potential long term partner or as someone to satisfy a curiosity or craving.  She knows the types of relationships she had before me would be destructive to me and to the kids. Her struggle is to contain an obsession.

We talked last night.  Difficult conversation for me to initiate because with W’s combative mood the past few weeks, my instinct is to avoid communication for fear of what it has been turning into. And I don’t want to have the role of “therapist” either.  She seemed like she wanted to talk and I did a good job of keeping the conversation productive.

I asked about this other woman, and asked if that if we were to have an open relationship was this the type of woman she wanted.  I asked if she was looking for a girlfriend or Just sex with a woman on the side.  That helped her open up some, and I learned this is probably is coming from a place of trauma and that she has never been able to have stable long term relationships or friendships because of an inability to control sexual urges and maintain boundaries.  after reading a book on poly relationships (suggested by the other woman), she felt validation that monogamy is not right for everyone.

After talking with her last night, she revealed that the current behavior and the behavior from her past is not about seeking pleasure or because monogamy is not what she wants.  It’s basically the push-pull of BPD.  I think most emotionally healthy people engage in sexual activity as an extension of emotional closeness.  What W described is that for her, sexual activity is to fill a void or to force an emotional closeness or satisfy a curiosity.  This current desire is probably rooted in loneliness and changes due to aging.  Healthy people can satisfy those urges through platonic friendships or hobbies or social groups. It seems that for W for her whole life that she tries to satisfy those feelings of loneliness through sex and knows no other way.  It sounds to me this is about wanting to feel emotional closeness outside marriage (as we all need) but not being able to separate sexual desire from the desire for emotiknal closeness.