Ramius

Marko Ramius was the captain of a Soviet submarine in the film "The Hunt for Red October" who planned to defect to the United States. In order to ensure that there would be no going back for himself and his officers, he mailed the Soviet high command a letter explaining his intent the day before his launch. In the context of a relationship, to "Ramius" is to purposefully take an action or say something that makes returning to your previous relationship impossible. The most common instance of this is to leave your old relationship for a new one, publicly making this move known to your now ex-girlfriend.