Welcome to the forums.
It seems to me that you're in a position of strength here. It is right and good that you want to protect your husband and marriage from pain and damage, even more so since your husband's desired OSO has violated your trust and damaged your relationships in the past.
But the heart is a wild and untamable creature, and your husband's heart yearns for this woman who hurt y'all. And you want your husband to be happy. So what can you do to protect what's precious to you while making room for the desires of your beloved's heart? I have a few suggestions for you to consider.
One thing you can do is work to make sure he understands in a deep way that you are PROTECTING and DEFENDING your home and hearts. And that you are completely committed to defending against all who would do y'all harm, whether the threat be physical, mental or emotional. And you need his help to do that. Get him on board with that. It's a clear and simple concept that every right-thinking person can embrace. (If he won't agree to work with you to protect and defend your home and hearts, you have much bigger problems that this OSO.)
Then, make 100% sure your husband understands that it's not his OSO as a person you object to, it's the pain and damage she causes by her (needy, untrustworthy, codependent) behavior. It's the behavior that must change in order for a healthy, happy, loving relationship to move forward, and ONLY she has the power to make those changes in herself. If she made the necessary steps to become self-fulfilled, trustworthy and emotionally stable, you wouldn't need to protect him from her, and the path could be open to moving forward together. But the work to be done is HERS. You cannot change her. And if you're smart, you won't pretend she's working on her issues if she isn't, and you won't be drawn into continuing her personal drama.
If her heart yearns for your husband as his does for her, she will do the work to be with him, whatever that work may be. If she is just looking for an enabler, she'll find another one when she realizes he's no longer available. In that respect, the ball is in her court. At any time, she can choose to start demonstrating the behavior of trustworthy, emotionally stable people. And when you know, by her words AND DEEDS, that she's serious about being the kind of person who can have healthy, loving relationships, THEN you are willing to move forward.
In the meantime, you can get together with your husband to make a plan to prevent future damage to your marriage. You write that he fell into a black hole before. What were the warning signs y'all missed or ignored before? What steps can y'all take to keep that from happening again? This is another opportunity to enlist his help protecting and defending your hearts and home.
Another issue to be addressed is your husband's desire to be with someone who has wreaked havoc on your lives. Why doesn't HE want to protect your home and hearts? Past behavior is the best predictor of future behavior, and this woman has done y'all harm. Why does he want to open y'all up to that again?
Another, much more machiavellian strategy you could consider is to be needier than her. Is this strategy open, honest and direct? Is it in keeping withthe highest goals of polyamory? Nope, not at all. But it worked in the case of one couple I know. The husband was caught up in an emotional black hole like the one you're describing, and his wife couldn't convince him to break free of the OSO's gravitational pull, even though she was destroying them emotionally, financially, even physically. When she had tried everything else she could think of, the wife decided to become needier than the OSO. She gave full vent to the frustration, rage and fear she was feeling because of the chaos and insecurity that had been brought into thier lives. Regularly, and very vocally. And especially if she thought the OSO was going to be calling with a "crisis". She started counseling to help her deal with the trauma. She gave every indication of a woman on the verge of a break-down (most of which was real, but some was not). Faced with the reality of having to choose between two devastated women, the husband chose to support and protect his wife. The OSO found another enabler. Be warned, though: the situation could have totally backfired and blown up in the wife's face.
Whatever you decide to do, best of luck. May your home be filled with peace, joy and much love.
Last edited by Fidelia; 10-27-2009 at 02:46 AM.
Reason: spelling error