The couplet means that intense heat killed the heart and liver, and that we nurtured our own enemies right next to us.

This profound couplet speaks to the tragedy of internal betrayal and the devastating cost of misplaced trust. The poet suggests that the intense heat—be it passion, suffering, or conflict—has killed both the heart and the liver. But the real blow comes from the second line: the realization that the greatest enemy was not external, but one whom the speaker nurtured right next to them. It's a poignant reflection on self-inflicted wounds and the betrayal of proximity.