It's been a long time since I've seen this fic, it might have been on Spark, but I had thought it was here on Dokuga. It's also possible it was on another site.
Here is what I can remember. It's an alternate universe,I believe the whole story was divided into two parts, the original and it's sequel.Sesshoumaru and Kagome are married and he is abusive. Eventually they had at least two kids. At one point Sess punishes Kagome by dropping his poison to burn and kind of infect her back. I also remember that the two kids have taken different attitudes toward Kagome, one adores her and wants to be around her and almost fears Sess, but the other sees how Sess treats Kagome and is extremely rude and disrespectful toward her.
At some point Sess and Kagome separate, maybe even divorce. Sess starts to date an adult Rin, but Sess still treats Kagome really badly. At some point Kagome begins to believe that Sess will hurt her again or even try to kill her. When Sess comes to Kagome to suggest that they work on their family and take a trip together (I believe Rin goes too), she actually writes good bye letters thinking he my try to kill her on this trip. While on the trip Sess sees his son's disrespectful treatment of Kagome first hand and reprimands him for it. I do think that Sess was planning to kill Kagome on this trip but, he begins to see how wrong things are in their family, and how dysfunctional he is.
The scene with the poison might be confused with another fic, but I do know the rest is all the same fic. If you have any ideas please let me know.