The speaker is jealous of something as ordinary as a tree. Leaves fall every autumn, yet they return, and that easy cycle of loss and renewal is exactly what the speaker feels they can't have. The glare in the first line is half joke, half grudge: it's a little silly to be angry at foliage, but heartbreak makes people irrational.
The turn comes with "but my heart fell for you." The poem plays on the word "fell," linking the leaves dropping from a branch to the speaker falling in love. The difference is what happens next. Leaves land and begin again, while the speaker's heart "smashed to pieces," a harsher, more final image than a gentle drop.
The mood is wistful and raw, with a touch of bitter humor. The trailing ellipsis leaves the thought hanging, as if the speaker is still sitting in the hurt and has no tidy ending to offer.