A babysitter is killed by having her heart ripped out on Valentine's Day and the Winchester brothers are on the case.
At first they believe the culprit may be a werewolf, but then when viewing footage from the "nanny cam" the clues point to a shapeshifter.
However, while their investigations are ongoing Dan Harper (Jim Thorburn), the husband of the family who happened to be having an affair with the sitter, is killed the same way.
But then Dan appears to come after his recently widowed wife, Melissa (Luciana Carro), and the Winchesters' discover they are actually dealing with a transmittable curse.
Unfortunately (or otherwise), the curse in Love Hurts is a blatant rip off of the antagonist from the popular horror movie It Follows, with scriptwriter Phil Sgriccia simply giving the central monster a name and substituting a "kiss of death" rather than sex as the method of transmission.
That said, it doesn't really matter as it becomes clear that what begins as a "monster-of-the-week" story is actually tied cleverly into the season arc, giving Dean a sudden moment of clarity about his connection to Amara and what that means the Winchesters' mission to stop her.