sensitive problem

Hy every1 plz give 2 mints for reading dis… I have a younger sister who is 17 yrs old. Nd she had many boyfrnfs.. Infct she changes 6 or 7 bf in a month.. Nw I came to knw dat she has make phycl reltns wid 3 boys.. My parents r so hard working.. Thy r making every effort to make our life happy.. And I don’t wnt to hurt dm by telling all dis.. Nd being an eldr sister I told her many tyms dat imprve urslf bt it dsnt make any diff on her behvr… Wat shld I do.. I don’t wnt to hurt my parents by telling all dis.. Plz hlp.