It's called a confounding variable.
Pretty much the first thing you learn in development psychology is that bad things correlate with bad things. Risk behaviour (binge drinking etc.) at a young age age typically correlates with mental health issues later in life. Other correlates for the two include negatively affective personality traits (like neuroticism in Big Five), as well as, you guessed it, unstable love life. This typically entails i) starting to date younger, ii) having more relationships, and iii) having shorter, less fulfilling relationships.
I doubt it was the relationships that ruined her, rather she just happens to be of weaker stock, and that can be seen in the way she dates.
