After love has ended, the speaker notices that being with the person she once loved has become ordinary. There is no magic when they meet, no miracle; they speak like other people do, and neither one can stir the other as before. That flatness stands against the past, when they seemed like wind and sea—restless, powerful, and full of splendor.
Now the speaker feels like a tide pool beside the shore: quiet, protected, but stagnant. That safety is real, yet it brings no happiness. In fact, the final stanza suggests something sharper—the pool is safe from storms and tides, but for all its peace, it grows more bitter than the sea. The mood is quiet and rueful, less like sharp grief than like a slow, empty ache.