I'm going to leave my friend alone drunk in berlin
Are you serious? How can you leave them drunk and alone in Berlin?
Let's just say I had my reasons for wanting to do that.
It sounds like you are leaving your friend in a dangerous situation. This puts them in a vulnerable position and you should not do that.
They are old enough to make their own decisions.
When someone is inebriated in an unknown location, it can be very scary and disorienting! How scared would you think your friend feel when they have no one to rely on when they're exposed? Why no stay with them, and deepen your relationship instead of weakening it?