Canon disproves this considering that Spongebob shows brief attraction to a mermaid in the first movie, and then no one else later. He’s either Asexual or has a weak libido.
The show's creator, Stephen Hillenburg, said years ago that SpongeBob is "almost asexual", so it's not as if Nick are retconning anything really. Anyways, one can be only 98% attracted to people of your same sex/gender and almost no one would claim that they aren't really gay, so I don't know why it can't be the same for asexuals, including animated sponges