I want to say I read it on Spark but it's been a really long time. I remember that Grandfather is actually Kikyo and Kaede's brother. When Kikyo died and burned the Jewel with her, he found it still in her ashes and took it and ran to the Well. He fell in, eventually met and married Kagome's mother. But after that, he suddenly aged to an old man. He had to like to her mother and say that his "son" had left but he would take care of her. Then she found out she was pregnant with Kagome. I hope this rings a bell with someone. I can't remember if Kagome eventually finds out either.

I meant lie. Not like her mother. Sorry!

The story that you are looking for is called "Love Has Nothing To Do With This", written by Shadowsweaver1 on Spark. Please note that this story is rated NC-17, so no YIMS.

http://www.dokuga.com/spark/story/5792/1

Thank you!