Love Allegory

A character uses an allegory to describe his romantic relationship with his significant other. Said allegory is usually rather up there, yet provides precious insight into said relationship from an unusual angle and is often ridiculously cute.

Although this trope is titled "Allegory", metaphors are also included.

Anime and Manga

 * In Natsuneko's Spicy Sweets, Yuu compares her relationship with Aki (a baker-in-training) to a cake of which she only takes a bite out of fear it disappears on her. Post-Relationship Upgrade, she dreams of the same cake and no matter how much she eats, it never grows smaller.
 * In Ame-iro Kouchakan Kandan, Seriho (owner of a teahouse) compares herself to a teapot who wants to make tea for everyone, and Sarasa, to a cosy that keeps the tea inside warm. Sarasa is slightly embarrassed by this story.
 * In Kannazuki no Miko, Chikane tells the story of a seashell, to which only one other seashell in the entire world will be a perfect fit. Especially poignant, since it is told to her destined Star Crossed Lover Himeko, though she is unaware of Chikane's feelings at that point.
 * In Totally Captivated, a deliriously sick Ewon tells Mookyul the reason he doesn't want to be in a relationship is because Mookyul is like the chocolate on top of a cake that he once stole because it looked so good but melted before he could ever eat it. Mookyul tries to convince him this is stupid and in this case Ewon can have his chocolate and eat it too.

Film

 * From Annie Hall: "A relationship is like a shark. It has to constantly move forward or it dies."

Web Comics

 * Xkcd:
 * Katamari.
 * Also, "Our love is like a Brontosaurus".

Video Games
""Definition: 'Love' is making a shot to the knees of a target 120 kilometers away using an Aratech sniper rifle with a tri-light scope.""
 * HK-47 of Knights of the Old Republic has a very unusual definition of love: