Alright, this FanFiction is AU and I don't really remember much of it. Sesshomaru is in love with Kagome but Kagome is in love with Inuyasha. Later Sesshomaru has to leave the country (for college?) and he gives his diary to Rin (who I believe is his adopted sister (maybe daughter)). Rin later gives the diary to Kagome and Kagome reads it. Kagome finds out that Sesshomaru was in love with her because he has poems after poems of Kagome in his diary.
He returns and she confronts him about it and they live happily ever after, I believe.