My sister-in-law has been in a sporadic relationship for the past three years with a boy she dated while in college. After they graduated from college the relationship ended, but they kept getting back together. I also think he was seeing one of my other sister in laws who supported this guy after he broke up with the older sister. There is a risk that he has had sex with the other sister who does not know the other has the STD's. Should the second sister be told by someone else or should the sister that has contracted the STD's tell her even though she desparately wants to keep it secret?