A long-term pattern of how a person thinks, feels, and relates to others that causes them or those around them real, repeating harm. Not a bad week — a way of moving through the world that's been stable since early adulthood.
Your partner has had explosive fights, dramatic breakups, and intense identity shifts since they were 19. Every job, every friendship, every romance has the same shape. That "pattern across every part of life" is what a clinician is listening for when they evaluate for a personality disorder.