She never actually fucked him. Even in the show she only really wanted to marry him, and that was because he'd been given a driver's license by Quimby, because Springfield is fundamentally irresponsible.
The only one who ever wanted to do sexual stuff with him was Shauna, and her age seems to vary between about 13 and 17 depending on the joke for the scene. That one episode was very unusual in drawing a character from the background out into a more rounded role.
I feel like the last time that happened with a character who stuck around and got subsequent episodes about them was maybe Apu? Or Smithers?