: Mortal +
Straight: Marty falls in love with Sue.
Exaggerated: Marty tries to kiss Sue but goes right through her as she does not have a physical form.
Downplayed: Marty sees a picture of the deceased Sue and feels a strong attraction to her, but Sue's ghost does not materialize.
Justified: Ghosts are sentient beings, too, and sentient beings can be in love.
Inverted: Sue falls in love with Marty.
Subverted: Sue knows they can't be together because they're in different planes of existence, so she tells Marty I Will Wait for You. In the meantime, Marty gets married to another woman.
Double Subverted: But eventually, Marty dies, and is reunited with Sue...forever.
Parodied: The Cute Ghost Girl Marty falls in love with resembles something on the lines of Casper.
Zig Zagged: ???
Averted: Marty and Sue are both living humans, or both ghosts.
Enforced: Our Ghosts Are Different
Lampshaded: "I love you...even if you are a ghost."
Invoked: Marty and Sue were in love, Sue dies, and Marty holds a seance to see her again.
Exploited: Marty's Uncle Evulz sends him to the house Sue haunts in hope that Marty will fall in love with the ghost and die, leaving his trust fund to Evulz.
Defied: Sue moves onto the afterlife. Marty moves on with his life.
Discussed: "So, how did your girlfriend die?"
Conversed: "Do you, Marty, take Sue to be your lawfully wedded wife until death do you... sorry."
Deconstructed: It's kind of hard to have a relationship with someone who has already Ascended to a Higher Plane of Existence, and to whom the laws of physics do not apply. (See "exaggerated", for example.) And what if she wants to go to the afterlife? And less-patient ghosts may not be so willing to wait for the Love Interest to die of natural causes.
Reconstructed: But there might be a way around it, for example, the ghost somehow getting into a physical body. Or simply serving as a Magical Girlfriend... Not being beholden to laws of physics can come in handy that way. And as for waiting for the Love Interest to die, well, ghosts have all the time in the world... And hopefully, patience.
Played For Laughs: Sue is mistaken for an Imaginary Friend, and everyone thinks Marty is crazy.
Played For Drama: Sue is mistaken for an Imaginary Friend, and everyone thinks Marty is crazy. Marty is committed, and dies alone in a mental institute.