Hello @angese10 - i don't think i've seen your previous thread here but based on this new post, i wanted to commend your noble efforts in fully considering the whole situation and for making your marriage work.
Everyone is capable of making mistakes and everyone is also deserving of forgiveness, if there is remorse. I also think you have a great head on your shoulders with your compassionate feelings toward the mother of your step son.
You are obviously thinking this through and it sounds like you want what's in the best interest of the child, but at the same time (and rightly so) you want what your husband wants (what makes him happy).
Your husband will obviously want his son with him for the most part - most parents will want that.
The birth mom, may not have been in a good place before, but her situation could have changed and if she made a mistake (of abandoning her son) before, does not mean she is not capable of remorse, repentance and a second chance, just as your husband deserved a second chance to work his marriage out with you. We don't really know why she's in that situation or why she did what she did -- we can't really know/judge someone until we walk in their shoes, right?
That being said, emotions are involved - your emotions, the son's, your husband's, the mom's. It's not easy to be rational when emotions are involved. I think your goal is what's in the best interest of the child and from your post (which will be subjective of course), it sounds like he's better off in your home (stable home) since we don't know anything about the mom's situation.
In the interest of fairness, you could perhaps offer a middle ground and ultimately let the courts decide... perhaps offer supervised time between the mom and the son? increase that supervised time a little over time, and perhaps advise the mom that while you understand her plight, she is welcome to spend reasonable time with her son, but that the courts are best to decide what is in the best interest of the child. Then she can take that on --- if she is able to demonstrate to the courts she is a fit mom and can provide a fit environment for her child, then she should be given the chance to be a parent to her child. This way, both sides have an equal opportunity to demonstrate their parental commitment to the child, to the courts.
I think if you refuse her outright or restrict her, she will feel more frustrated, perhaps angry, desperate and what not - who knows what that could lead her to do, and how that might impact the son. Repression is not a good feeling. I really think the first and healthy course of action is to share the child, for now, as long as she's not causing harm to the child.
I hope you find answers and peace with this situation soon... it takes a noble and beautiful spirit to forgive the woman who was involved with your husband. But honestly there is serenity in knowing you did yourself and everyone around you good. Anger, revenge, are not good things to carry in your heart so i think you're in the right direction.
Good luck sis sana you can update us. *flowers*