It would be hard to find a more important theme in "The Highwayman" than love. The love that Bess and the Highwayman share drives all the action, and, without it, there really wouldn't be a plot. Even if their love ends up killing them, it's clearly supposed to be a beautiful thing. Then there's Tim the ostler. He's in love too, but his love is much weirder and darker, a big contrast with the exciting passion of Bess and the highwayman.
Love is a both a beautiful and a destructive force in "The Highwayman." This contradiction forces us to reconsider our thoughts about the role of love.
The ghost story at the end of the poem softens the blow of the violent deaths, and makes it clear that the speaker is most interested in the beautiful, comforting aspects of love.