She is trying to keep in the wings and trying to make me feel sorry for her. and I want her to let me go.
She's not going to let you go if you keep responding with guilt. For the most part, Borderlines don't suffer from guilt, they suffer from shame. Guilt comes to those who try to leave the craziness behind.
You need to trust letting go for now. If another Man has been brought into the drama - this person is a "transitional object" that is similar to a security blanket- in order to soothe the Borderline's feelings of abandonment from erupting due to your perceived withdrawal. Don't get hooked into the deception of the manipulative comparison that this other person can give to the Borderline what you cannot.  :)on't attack, retaliate or get into a battle with this person because they have completely separate issues of their own that haven't got anything to do with the underlying issues of your wife.
Stop enabling her by feeling sorry for her. She needs to suffer the consequences of her behavior without you rescuing her. She needs to learn from the process. You have to protect your feelings by detaching from the drama. Do not play into the triangulation
(read definition). You may feel you are being wrong for not speaking up about your hurt, but realize that you are actually being healthy by not engaging in a debate with a person who refuses to hear your side. You are now putting boundaries into place which will stop you from being wounded again. Good luck~