For the life of me, I can't remember the author or the name of the collection. It is a one-shot collection with several stories. One of the collections is called Favorite Author. Another story group in the collection is when Sesshomaru takes Kagome as a mate, not telling her that he is already mated to a female demoness. In this one, the first mating is for power/politics/etc. and the second mate is for love. Kagome doesn't agree with the Feudal mating rules regarding this and considers herself a homewrecker/other woman in the mating. I know that I read the collection here. I can't remember anything else in the collection. Thanks in advance for your help!

I think you're looking for "It's a dog's world", by Kanna37.
The link to the story's here: www.dokuga.com/fanfiction/story/5970/1
It's rated MA.

And you are absolutely correct. Worst thing is that I have that story bookmarked under favorites...

Thanks for your help!