Kurt is talking about his addiction to heroin in the first four lines. He says "she eyes me like a pisces when i am weak". Speaking about coming down off of heroin and being weak from it. The heroin is just eyeing him down until he uses again and is back "up" on his binge. "ive been locked inside your heart shaped box for weeks". His love for the drug has locked his soul into a metaphoric box of only caring about using. "i've been drawn into your magnet tar pit trap". Again saying that he is trapped by the heroin(which is a tarry substance) and by using the words drawn, magnet, pit, trap all in the same line he gets the point across of how addicting the substance is to him. "i wish i could eat your cancer when you turn black". He mentions it being cancer which is something that kills people but he says that he loves it and would eat the cancer. Its something that he "loves to hate" or atleast he acknowledges how bad it is for him but he still loves the high he gets when using.