KRYPTONITE

KRYPTONITE...Slowly kryps its way deep into you skin, you see the signs but you turn a blind eye.Then it becomes a stuggle for control from the outside when you really seek to fight the inside. The state of helplessness, the poisonous,yet sweet taste of what you once called love. 

According to urban dictionary;
A man/woman that calls someone their Kryptonite means that they are their weakness. Someone or something they have to stay away from because they want it even though it's not good for them or will hurt them.
Someone you want but can't have can be called your Kryptonite.