A SpongeBob SquarePants fan theory explains why Squidward hasn’t moved away from SpongeBob even though he’s always annoyed by him, and it’s because he was literally paid to look after him. SpongeBob SquarePants follows the daily adventures of the title character – a sea sponge that looks more like a kitchen sponge – and his friends (and enemies) living in Bikini Bottom.
SpongeBob is often accompanied by his best friend Patrick Star, his friend Sandy Cheeks, his boss Mr. Krabs, and his neighbor (though not exactly his friend, despit SpongeBob considering him one) Squidward Tentacles. Squidward is always annoyed by SpongeBob’s existence, and yet he hasn’t done much to move away from him - except for one instance in which he moved to Squidville, but that didn’t go well.
Interestingly, a fan theory, posted on Reddit, explains why Squidward hasn’t been able to move out of his house and stay as far away from SpongeBob as he would surely like to: Squidward is SpongeBob's guardian, and he watches over his neighbor as a favor/debt to SpongeBob's parents who may have helped him get his own life back on track after his failed clarinet performance derailed him.
Squidward Is SpongeBob’s Guardian
The theory takes a look at Squidward’s backstory and connects it to SpongeBob’s to explain why Squidward is still part of SpongeBob’s life. Squidward is a classically trained clarinet player and went to school with Squilliam Fancyson, so he was part of high society at some point. After a bad clarinet performance, Squidward’s confidence crash and burned, and he was essentially kicked out of his circle. SpongeBob, on the other hand, is believed by many to have a disability, which would explain many aspects of his life. Because of that, SpongeBob’s parents (who are living off a generous inheritance) paid off his house and are letting him live alone to give him a sense of freedom. This is also why SpongeBob can support himself economically without a problem even though he works at a fast-food restaurant owned by the cheapest boss in the world.
It's possible that SpongeBob’s parents knew Squidward from his “high society” days, and were aware of his social decline. In order to help him, he was given a loan to get back on his feet, under the promise to keep an eye on SpongeBob, just to make sure he’s safe. Squidward’s annoyance is because he always has to make sure SpongeBob won’t harm himself (with poor Squidward often ending up being the one injured), and SpongeBob isn’t exactly the most careful and calm individual. Maybe Squidward’s house isn’t really unsaleable, and he just owes to SpongeBob’s parents after they helped him in his time of need.