<human>: My fiancé and I threw a pre wedding party Friday and her sister decided to tell me she uses cocaine and asked if I cared if she went outside and got high. I was drinking and responded the way I would respond to most people I don't feel very close too ( go do whatever you want). 

After the party I realized what she told me and decided to tell my fiancé. My fiancé freaked out more than I anticipated. I ended up downplaying the whole thing. Telling my fiancé she's just experimenting, a lot of people do, it doesn't mean they will become addicted or go to jail (her main concerns that night). To my suprise she backed off and hasn't mentioned it sense. 

At this point, I'm starting to feel guilty about downplaying this. I ran it by a coworker and she said I should absolutely tell her parents because her son is addicted to meth and it started with cocaine and she just wishes someone would have told her when it first started. 

My concern is if I do tell her parents or have my fiancé tell them they will blow this into a huge mess. Maybe I am naive but I feel like a lot of people go through stages like this.. I also don't want to ruin the trust her sister has for me. 

I just don't know what to do at this point. Do I leave it alone or let her parents know?

Can you provide a brief overview of the text?
<bot>: Fiances sister told me she uses cocaine. Do I tell her parents or chaulk it up to a phase and leave it alone