I was a stepmother to a young boy who I helped raise for 6 years. His father, my XAH, was the abusive alcoholic. I did what i could to protect my stepson from his father's drinking, but in the end, I had to leave to protect myself and my infant child. It tore me to pieces and I often posted about this here on SR.
I do not have a happy ending for you. Even though I was a mother figure to my stepson for all those years, I had no legal rights to him. To punish me for leaving, my XAH forbade me from contact his son. In an interesting twist of fate, once I left the household, my stepson chose to leave his father and to return to his mother's. That's when he contacted me, asking me questions and begging for contact. I wrote a long letter, sent him photos and thought that we could begin corresponding, but unfortunately, my XAH intervened again and convinced his son that I am poison.
At this point, there isn't anything I can do, legally or otherwise. I made myself clear to my stepson via email. I never villified his father to him, and I plainly told him how horrid I felt for leaving him behind. I gave him every bit of contact information I have, and invited him to contact me if and when he wanted to.
Right now, he's still young (13) and no doubt still under his father's thumb. I hope that one day, he'll be able to contact me and resume our relationship. I also hope that my daughter will get the chance to know her half-brother.