As the episode goes on, Patty becomes more deteriorated. Green stench comes out of it and Patty is looked to be squashed and off-color. When SpongeBob is singing to it, it falls in the water, which makes it fall apart and start to smell bad. It becomes even more rotten by that night at the Krusty Krab.
Role in episode
SpongeBob made a perfect Krabby Patty that he had named Patty. She would have originally be a tough fish's lunch, but SpongeBob did not want her to get eaten. SpongeBob gives the fish a grilled shoe burger instead and takes Patty to his home.
Patty then has a makeover and hair-cleaning and goes on an adventure with SpongeBob while the latter sings the song "I Can't Keep My Eyes Off of You" to as they get attacked by hungry scallops and fall into the end of a waterfall.
Unbeknownst to SpongeBob, Patty soon becomes disgusting, smelly, rotten, and is so terrible looking that people run away from it. Then, SpongeBob realizes that he must eat Patty, which he does, and due to the repulsive condition of the burger towards its final days, asks Mr. Krabs for a doggie bag.
Relationship with SpongeBob
While SpongeBob is in love with it, it does not really have any feelings for SpongeBob since it is a sandwich and is thus insentient. SpongeBob is very much in love with it until he realizes that Patty rotted while he was at the Krusty Krab. After Mr. Krabs tells him about the true purpose of Krabby Patties, SpongeBob then eats it despite its spoiled condition.
Relationship with everyone else
While SpongeBob falls in love with Patty, everyone else knows that it is just a Krabby Patty and are therefore not fond of SpongeBob's love with it.
Patty is seen on the DVD cover of To Love a Patty, dancing with SpongeBob, even though he is holding it.
Patty is the only "character" SpongeBob has fallen in love with. It should be worth noting that Stephen Hillenburg confirmed that SpongeBob is indeed asexual, however this is not synonymous with having no romantic feelings.