The speaker reassures their lover that they don't need to worry because the speaker will fill them with love that no one else can. The speaker promises to always be true and that the lover does not need to hate the world or fear being alone because the speaker will love them forever. The speaker knows their lover does not want to experience sadness, arguments, or a break up that would cause sorrow, so the lover does not need to worry because the speaker's heart belongs only to them.