It's all about love in this ballad, but it's the kind of love that teaches the speaker some tough lessons about life. As a young and foolish boy, he just can't get the whole notion of taking things easy. He probably needs to have everything happen right away, as quickly as possible, without scrimping on the passion part. But love, like the girl says, just doesn't work that way.
Lines 5-6: The girl tells him to take love easy like the leaves growing on the trees. It's a nice simile for love since you can't rush matters of the heart. Love needs to happen naturally, in other words.
Lines 7-8: Of course the speaker doesn't take the girl's advice because he's young and foolish. So the speaker may be foreshadowing some sort of disappointment or heartbreak later on.
Lines 15-16: By the end, after not taking the girl's advice on love twice, the speaker ends up full of tears. So he learns a hard lesson in love that makes him realize that maybe the girl was right about taking things easy.