I read it awhile ago, so I don't remember much. Basically Kagome leaves Inuyahsa, but doesn't tell him why. 500 years later she ends u working for him(in America I believe) and he tries to make her life hell. It turns out she left him to work on something to prevent the loss of their future children since hanyou births are so rare, and Inuaysha comes to realize she left him to help them. At the end it turns out HE sends her down the well to end things with his past self so they can be together in the future.
Sorry, I know it's a little all over the place, but it's what I can remember. If anyone knows what this fic is called, I would very much appreciate it :)