Here is a single sentence, and it holds a whole puzzle: the speaker is lying right next to someone, and still feels "miles apart from her lips." The distance isn't physical. Their bodies are close, but something between them makes a kiss feel impossibly far away.
The poem doesn't tell us why. Maybe the relationship has cooled, maybe there is something unspoken, or maybe the speaker simply can't bring themselves to reach out. The text leaves that open, which is part of its power. What we do get is the feeling: loneliness, longing, and perhaps a quiet sadness at being so near and so shut out.
The mood is hushed and still. Because the poem is so short, the silence around the line feels like part of it, the way a pause hangs in a room where nobody speaks. The contrast between "beside" and "miles" does the heavy lifting, turning a small gap into something enormous.