Shame

Subject: a man who only cared about himself hurt a woman, and he feels horrible shame for it.

Tone: sorrowful.
Untender: demonstrates how little he cared about the girl's true feelings.
Boatloads: describes how guilty he feels through a figure of speech, and also has a sort of southern feel to it.
Overwhelming: expresses how he feels so guilty he cannot live with it; it consumes him.