At a lose to my problem, we have been together for 10 years?

it is easier to put a point across by discrediting my partner but that is not the truth, the truth is her daughter had a second child after having a mental breakdown and losing her elder child to her ex-husband. Now we have the other child, a dear little girl, and have had her for the past 3 years. This may sound selfish, but at 52 with 2 grown sons I don't want to be a full time baby-sitter, as she is growing up her needs are becoming increasing harder for me to meet. The only reason I have not left is that I believe the child has become dependant on me emotionally and I don't want to hurt the little mite. Oh,dear what a mess.