The speaker describes a kind of love or intimacy that feels more like an illness than a comfort. Howling in someone's arms is raw and animal, and comparing it to a heart condition suggests something chronic, something carried in the body that can flare up at any time. The next image deepens that idea: this closeness is as familiar as tobacco, a habit people know is bad for them and keep up anyway. The poem even says people plant it "to be miserable," which sounds bitter and a little darkly funny.
The last lines are more puzzling. "Eyes weary of the light / in a pipe" could mean tired eyes staring at a glowing bowl of tobacco, or a worn-out person watching something burn down. Judging by the imagery, the mood is one of resignation. The speaker seems trapped in something comforting and harmful at once, and too tired to pretend otherwise. The title, "Allopath," hints at a clinical, treatment-minded view of this ache, though the poem leaves it open.