Dear Liz, you have made it abundantly clear that you wish to remain in the marriage. You also have expressed that you are unhappy.
As you know, of course, you have free will to do what you want. You can stay forever, and nobody here is going to tell you to leave.
As far as I can see, those who choose to stay (as well as those who end up letting go) have one path that seems to work toward their happiness. That is commiting oneself to a 12-step program (Ex: alanon) and really working all the steps, along with help of a sponsor. REALLY working it--not just dabbling the toes here and there, or learning just enough of the "right words" to keep everyone at bay. Tha t would be like an alcoholic dabbling at AA. LOL.
You say that you have a personal therapist---I am assuming to work on issues arising from your abusive childhood and continuing abuse. Most of the people on this board that speak of long term recovery seem to have the same. Family of origin work seems to require the same committment as working the 12-step program. The best therapist in the world can't do the work themselves.
It seems to me that this is the path to personal happiness---rather than spinning wheels playing games with marital therapists. Direct the energy where it will do the most good.
If you can't make this committment for yourself---could you do it for your son? This is the one who is being damaged the most---as we all know, the children suffer the most.
dandylion