Lyric discussion by traumahound 

Cover art for O' Sailor lyrics by Fiona Apple

She's the "other woman" in this song. She waited patiently for him, probably assuring her that he was leaving his wife, all the while dragging her deeper into love with him. Eventually he's had enough of his paramour (his adulterous lover) and let's her go by the boards (discards her, like something fallen overboard and carried away, thus the sailor reference.)