So the uke is in love with a married man that he works with and he acts like a mistress. The Seme ends up getting a divorce to be with the uke. It was a really cute story and I really want to read it again~
uhmm this may or may not be it http://www.mangago.me/read-manga/kyuuso_ha_cheese_no_yume_omiru/
That sister was seriously annoying -_- more than most girls in yaoi
Yet it was all thanks to her that those two got together... :)