Mabel Pines was 18 years old and a young lady with a future. That was unlike Dipper, who was an alcoholic who had sex with many prostitutes.
One day, a Mabel's boyfriend, Marc, drank some beers with Dipper
Both drunk, they started making out in Dipper's room and started tl get were having sex and they were very good at it.
"Dipper, mabel is a virgin and I don't want to do anything to her...I promise. I am bisexual" he said in the beautiful act.
"I am gay" Dipper answered.
Mabel then saw both of them naked a doing homosexual acts, so she screamed and called Pacifica (Dipper's girlfriend) to tell her what happened.
Then Pacificaarrived and slapped Dipper and kissed him even if he was gay because she did not know if course.