Help with an old doujin

I read it awhile back, there was some kind of "disease" where people were connected by a "red string of fate" that would connect to someone had a crush with and at the end of it after the main characters have sex there's became a heart.

Took me a bit to find because of odd title. Euryops Daisy by Otsuka Kotora. It is the 5th story in the Angraecum tank.