He had already told them pompously that he was only staying over Christmas because it was his duty as a prefect to support the teachers during this troubled time.
Retiring oneself voluntarily, in order to save others (and oneself) from the consequences of one's own inner emotional turmoil is the true sign of a great and kind soul.
If they're not, Britain could separate from the EU in what's called a No Deal Brexit but without an agreement in place, that could create some temporary instability for both Britain and the European Union.
Worries about a trade war have caused the Dow Jones Industrial Average of 30 significant stocks to take some major dives recently, losing hundreds of points in a given day.