My boyfriend and I have been together for almost six years, in NY. He has a daughter who is six years old. He has full custody of his daughter and she has been living with us since she was about 2. Before that he had visitation. The mother was found to be neglectful of her daughter and custody was taken away from her, which she also signed off on. She has supervised visits with her daughter every other week at her mothers house. The mother is supposed to pay child support but is in arrears by about 10,000. I have been in his daughters life since she was 4 months old. I have been raising her as my own. I want to know how I would go about adopting her. Also, I want to know if for some reason he and I separate will that mean I owe child support? Lastly, what legal rights do I have if this adoption does not happen and we separate?

A step-parent adoption cannot happen until you are a step-parent. To become one, you have to marry your BF.

At that time, if you want to adopt you probably are going to need the permission of the child's mother.

If and when you do marry, and adopt the child, you would be legally the child's mother, including having the duty to pay child support should you subsequently divorce or separate from the child's other parent.

First, as noted, to do a step parent adoption you have to be a step parent. Second, to adopt the mother would have to agree to it. Once these two hurdles are passed, you would need to get an attorney to file the adoption petition.

An adoption transfers legal parentage to the adopting parent. So if you do adopt then, yes, you could be liable for child support if you split.

Right now you have no legal rights pertaining to his daughter. Until and unless you adopt her, that will not change.

What if we choose not to be married? Are you saying I cannot adopt her?

Do I have any legal rights to her as I have been supporting her, raising her, etc if we separate?

Well it appears that in NYS you do not have to be married to adopt your partner's child. http://www.inmotiononline.org/assets/pdfs/TheBasicsSeries_English/Adoption_in_NYS.pdf NY is unusual in that regard.

So you could petition for adoption, but the mother would have to agree.

As I said, though, until and unless an adoption is granted you have no legal rights pertaining to the child.