I have a feeling this connects to Pink Diamond in some way;obviously non-rebel gems are very loyal to their diamonds,and since its been revealed that Jasper was originally in Pink Diamonds allegiance,I don't think her siding with Yellow Diamond was consensual.I'm guessing this caused some major psychological damage on Jasper and she has it in her mind that even unhealthy power will help her avenge Pink Diamond,or something like that.But idk,I'm not the best at theories.
We have lost even this twilight. No one saw us this evening hand in hand while the blue night dropped on the world. I remembered you with my soul clenched in that sadness of mine that you know. ... The book fell that always closed at twilight and my blue sweater rolled like a hurt dog at my feet. ... Always, always you recede through the evening