And you take the blade right out my heart, just so you can watch me bleed
This girl is sadistic, and loves watching JT suffer throughout their relationship.
Using a metaphor, JT describes his treatment at the hands of this girl. She does things that “stab him in the heart,” such as flirting with other guys. She then “removes” the blade, maybe by insincerely apologizing. Removing an object from someone who is bleeding causes the bleeding to worsen, so by her meaningless apology, JT is still hurting.
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