So there was a fic where Kagome and Sesshomaru get together and combine the packs, and everyone knows they're a couple except Jacken cus his sense of smell isn't that great so he can smell a female on his Lord but can't tell who it is, and one night when Kagome offers to comb Sesshomaru's hair Jacken snaps at her about how the female demoness his Lord is courting should kill her and everyone just kinda looks at him. That's all I remember.

I think you're looking for one of these? Both have kagome and sesshomaru becoming lovers. I remember the scene you're describing but can't remember if either of these are right.

A Taste Of Perfection COMPLETED
RATED MA
Things go from complicated to downright ridiculous as Kagome finds herself the focus of one overly curious dog lord’s interest. Can she juggle all the responsibilities that come with being the shikon miko AND the attention of a daiyoukai?

A Blue Ribbon COMPLETED
RATED MA
It all began with a blue ribbon. She sparked his curiosity with her peculiar habits. He awakened her lust with his alluring nature. Can this develop into something more than mere physical attraction?

It was A Taste of Perfection, thank you so much!