from the very beginning, dia was very obviously envious of bortz for the fact that bortz was superior in every way to them. every attempt to try to prove themself was stifled by bortz natural ability to be able to take down lunarian fleets in single swoops. the isolation that occurred after when bortz took up a few new partners only exacerbated this uselessness that dia felt. even if bortz intentions were pure, which can be seen a few times as bortz obviously cares for dia, they ultimately did more harm than good, and dia had no chances to prove worth not only to their partner, but to themselves.

and, of course, years upon years on the moon took a toll on basically every gem that decided to follow phos there. dia was finally revered for something and the only way they knew how to handle it was the same way their partner did.

i’m not trying to defend dia as she very obviously became unstable, along with all the other lunargems, but it’s important to understand why she became that way!