Relationship Advice? My bestfriend just had sex with a guy who is too old for

[My-My]

her and that she doesn't no...? Please tell me what I should do. My best friend which is 16 just had sex with a 23 year old who is no good. We were on a school trip and this was a random dude that one of our other friends knew and they just up and decided to have sex. It takes 2 to tango and I know he did not force her into having sex because she was following him. It felt terrible to see my best friend have no respect for herself and me. I don't think I want... or need... her to be my friend anymore. If she's going to act like a hoe she will be treated like one. And when I talked to her about it she didn't really seem to care. I was like duh this dude only wanted you for sex and you willingly gave it to him. She only said she felt like crap. Little did I know that she has had sex with with 2 other boys and never told me, her supposedly "bestest friend" a couple of months ago. Should I kick her to the curb? Do I need to tell our teacher just in case something comes up and what about her parents? All advice is appreciated.