It wouldn't be a betrayal if your kid asked for it. Your anger would be a bit misplaced. Better to lay into your own kid, and let his friend's parents deal with their kid.
I don't care if my child begged for it. He supplies drugs, he's toast.
And if this 19-year-old "kid" has sex with your 11-year-old because she "asked for it", you would give your daughter a stern talking to and let his parents deal with him.
Don't look for a card from me this Sunday.