The speaker describes a relationship in which quiet has become a problem. Someone, "she," doesn't realise that silence between two people can change love as surely as shifting weather changes a landscape. The line "in bed it kills" is blunt and sudden. It suggests that the closeness of the bedroom is exactly where the silence hurts most.
In the second part, the speaker lies awake. Her smell is still beside his pillow, so she is physically near, yet that comfort doesn't help him sleep. He seems to be nursing a wounded ego, perhaps from an argument or from something left unsaid. By morning they "part... like aliens," as if they were strangers from different worlds rather than lovers. The mood is cold, tense, and quietly sad. Nothing dramatic happens, and that is the point: the distance grows through what isn't said, and the speaker seems unable to break it.