The phrase "three thousand floating worlds, three in my love" comes from Twilight. What does this poem mean?

This sentence comes from Twilight City, and the original text is "Three thousand floating worlds, I love three, the sun and the moon are green, and the sun and the moon are dusk, and the youth is morning and evening". This is a confession, which means that there are three things I like best in this world, the sun, the moon and you. I like the sun in the morning and the moon at night, and I will always like you.