I would've posted this sooner, but I'm still post- Mabelcorn.

First off, I'd like to take some of the Pines' twins words.

"They used to be like us, but then they got all stupid. Promise me you won't get stupid?" -Mabel

[Promise me you'll tell no one, nor even your sister.] "...I promise." -Dipper

Most notably:

"You've been spending a lot of time with old Fordsie lately," -Mabel

And the most eminent:

"Trust no one, trust no one!" -Dipper

It's my theory that the discovery of Ford(and everything else) has caused a rift of it's own, in their relationship.

Dipper: In three words, without even knowing he existed, Ford completely RUINED Dipper's life! Now, Dipper will never again Trust anyone.

Mabel:She's already been protective of her relationship with her bro, and meeting Ford doubled that insecurity.  She's so insecure, she's a part of the problem.

These twins are both corrupt, and a fight will happen soon.

To make up for the depressing chapter, next time will be a SU theory!