This is an older fic I read on ffnet.Not sure if I remember it all correctly.
Basically, Kagome was found by Inutashio as a child and given as a gift to Sesshomaru. When she came of age he started using her as a concubine. As time went on, he mated, but his mate couldn't produce an heir. He ends up getting Kagome pregnant, and after she delivers he takes child away from her and gives it to his mate. Anyhow it ends so that his mate kills herself and Kags&Sess end up together.
I can't remember the title, and may have gotten few details wrong.
If it rings a bell please let me know
Tnx