4 ideas
The man describes a life, and a marriage, spent chasing aliens who never desired him in return: his wife was lost to the same obsession, and he now works menial jobs on the station just to stay near them. His confession is itself a warning, yet the reporter still feels the pull toward the aliens as the story ends.
The story argues that humans are wired to seek the stranger as a mate, a reproductive drive that pushes toward genetic outsiders. Aliens are the most extreme stranger possible, so they trigger this drive at full strength, but they cannot complete it. The result is a desire that can never be satisfied and so never shuts off, which consumes people instead of renewing them.
The spacer recasts first contact through the history of island peoples who met European ships and gave away their land, customs, and self-respect for manufactured goods. In this reversal humanity is the dazzled native culture, and the aliens are the indifferent visitors. The damage comes from the contacted people's own hunger for the foreign, not from any hostility by the aliens.
The title echoes Keats's 'La Belle Dame sans Merci', in which a knight is seduced by an otherworldly lady and wakes abandoned on a cold hillside. Once someone has longed for something that doesn't care about them, human partners and ordinary life feel flat, so the person is left both unfulfilled and unable to return. The one who desires is emptied out by chasing something that does not even notice them.