Rotting song meaning

The narrator of this song is a person who is dying from an illness - either physical or emotional. It's destroying him and makes him feel like he's "rotting inside". Whether it is a physical disease that is damaging his body making him feel like he's falling apart, or an emotional state that drove him to the edge and is now physically killing him - it is a condition which will obviously lead to his death, and he knows it. "Kiss me one last time" - he's ready to die, because he's tired of "rotting".