In the first season episode The Jerusalem Duality (2008), Dennis Kim already predicted that string theory was a dead end, and that Sheldon would eventually see it as well. It took Sheldon an additional six years to come to the same conclusion.
One of the fields that Leonard suggests for Sheldon to study is Loop Quantum Gravity. Sheldon once started a fight with Leonard's ex-girlfriend Leslie Winkle (Sara Gilbert) over the superiority of String Theory over Loop Quantum Gravity in The Codpiece Topology (2008), so it is not surprising that he shoots it down immediately.
This episode elaborates on why Sheldon has such a disdain for geology. In The Skank Reflex Analysis (2011), he called it "[not] a real science", and here he compares it to the Kardashian family, implying that geology is shallow knowledge, or doesn't require talent.
Title Reference: After advice from Penny, Sheldon starts to treat his giving up of string theory as a diremption (separation or split) between him and his work, like breaking off a personal relationship.
This episode was taped on March 25, 2014.