You're the child of Ford and it wasn't the greatest thing after he disappeared through the portal and now he's back.

You tried to connect with him but it was clear that it wasn't going anywhere and when he took Dipper on a mission it kind of hurt.

You and Mabel were together waiting for the two to come back but you both overheard Ford taking Dipper under his wing.

It hurt you a lot more and it felt like you got replaced so when he came back you confronted Ford about it.