This is a song about a woman who kept going back to a man who kept hurting her and she decided she can't move forward in their relationship. She learned to get over him and he promised to never hurt her again. She's moved on from him. He's cold hearted and she doesn't need that. Though she's moved on a first heartbreak always hurts and remains as a scar. She likens her ex to a serial killer killing all of the girls he's dated and keeping a collection of their hearts in a jar. Of course one could argue that she is talking about depression. Though I feel it also includes a hint of overcoming depression.