You decide to just let it go and eat the cost of four wasted bottles.
While a kind gesture that nets you a loss of eighty-three bits, it's never repaid—and he never comes by your bar again. The rumors spread like wildfire, however, and business prospers as everypony comes to try to find out from you what Prince Blueblood's story was.
Eventually, they accept the fact that you never share the secrets you learn from your patrons, and life continues on as normal, as if it had never even happened.
But, of course, it did. You know the prince's feelings he's locked away and the pain he's putting himself through.
And there's nothing you can do about it.