Bill manages to piss off a witch and gets put under a love curse, that causes him to fall in love with Dipper.
After days of Dipper getting frustrated with Bill’s ideas of flirting, animal teeth and skulls, offers to torture and kill his enemies, bouqets of poisonous flowers, Dipper either reads about the love curse in the journal, or he meets the witch that Bill pissed off. From here on, the cure for the curse would be one of two things:
A true love’s kiss, which basically means Dipper needs to fall in love Bill and kiss him to break the curse, or a potion that can break the curse if Bill drinks it.
In the case of the first scenario, Bill wouldn’t know that Dipper and
Mabel were trying to break the curse, so when Dipper starts spending
more time with him willingly, he’s ecstatic. And slowly, but surely,
Dipper starts falling for Bill, and even forgets that he started doing
all this to break a curse. So, after dating for two months, they’re
having a picnic in the forest. Dipper kisses Bill, and Bill pushes him
So, with the second option, Dipper and Mabel gather the ingredients for the potion and brews it, but when it’s done Bill refuses to take it, saying he likes to be in love with Dipper and doesn’t want it to stop. So Dipper, without Bill seeing it, puts some of the potion in his mouth, and kisses Bill to transfer the potion to him, ending with Bill pushing him away.In both cases, Bill is furious and leaves immediatly. In the first storyline, Dipper is heartbroken, in the second he is relieved. But stories would end with Dipper waking up the next day, to find a deer skull on his desk.