Standing at the edge of the sea, the speaker lets their mind drift to someone they miss or long for. The poem is built on one repeated line, "I dream of you," which works like a heartbeat: the thought keeps returning no matter what else is said. The speaker pictures "another life we could lead," which suggests the two are not together now, or that something stands in the way.
The feelings are mixed. A moonbeam in the rain is beautiful but faint, and the speaker also calls the dream "a fantasy" and "a pain," so the longing hurts as much as it comforts. Yet the dream is "easy" and "careful," as if the speaker handles it gently, afraid to disturb it.
The ending is quietly hopeful. "If dreams were true" admits that this may be wishful thinking, but the speaker hopes the other person dreams of them too. The mood is soft, wistful, and a little lonely.