Here "violet hill" refers to a snowy hill turned violet from the blood of those who died in the war, and after running away he's returned and taken his love there to show her why he had to desert the army and what he faced and suffered. But now the army is after him for deserting, and thus again he will be apart from his lover. So again desperately he asks his lover that if she loves him she better let him know for she may never see him again. Also here the piano is the only instrument playing, to highlight the sadness and the coldness of the situation.
Violet Hill is a person