When did Sollux & Feferi get together? Did Feferi always have feeling for him and he decided to be her matesprite?

Feferi mentions that they’re in a quadrant in this flash and Erisolsprite refers to one half of himself as being her former matesprit when speaking to Fefetasprite on this page. It’s likely that they only became matesprits after sgrub had begun but the details of their relationship and how it started aren’t shown in-comic.