Tribute to my teenage love

At what point does a sweet boy become a villain?
How does this switch just happen, slowly or quickly?
When does a romance turn into a thriller?
And the role plays you, and there is no way of quitting?
How could a saviour grow into a psycho?
What should I do now, keep loving or start decamping?
Am I a bad girl, too, since I used to like you,
And since we both have never, ever been happy?