Autumn, in this poem, is two things at once: a season and a lost love. The speaker starts with a simple fact, that leaves fall in autumn, then makes it personal by saying they fall too. The repeated "fall to the ground" links the leaves to the speaker's own collapse, and blames it squarely on autumn.
Then the poem turns openly to love. The speaker says they loved autumn, and that she was "the love of my life." Because the season is called "she," it reads like a relationship that was always going to end, since autumn "doesn't stay for ever." What remains is the image of a tree without leaves, which is how the speaker seems to see themselves: stripped, exposed, left behind.
The mood is quiet and sad, with no anger. The short, broken lines feel like halting speech from someone trying to say something painful plainly. The last word, "Behind," is left alone on its own line, so the loneliness lingers.