Someone is still deeply in love, even though the feeling no longer seems to be returned. The speaker keeps repeating "I'm falling," as if the word were a loop they can't climb out of. It suggests both the rush of love and the helplessness of being pulled down with no way to stop.
The poem's quiet pain sits in two lines: "When I see how you don't see me anymore" and "Eyes seeming so familiar, when they are not." Together they suggest a closeness that has faded. The person once known so well now feels like a stranger, yet the speaker still gets lost in those eyes and in "your favourite song," a small detail that shows how much they still hold onto.
The mood is wistful, tender and a little sad. The opening and closing lines almost match, which leaves the speaker exactly where they began: devoted, and stuck.