Tell me why.

Why is it that all the best things fade?
Nothing stops time, no plan yet laid.

Why do sakura fall at their very best?
With them the joy of spring set to rest.

Why is it that childhood must end?
Growing cynical knowing no friend.

Why do sweet songbirds leave you?
Nature made harder than it needs to.

Why is it that snow must melt away?
The dreams you dreamt couldn’t stay.

So tell me why this is the case,
That all good things leave this place?

The first thing that throws me off is the title. Paradise Lost is the name of the epic poem by Milton. I'd consider finding something more unique, and less attached to an incredebly well known work. Instead of making me think of your poem, the title makes me think of his. I also think you could find a title that better fit the poem overall.

The poem could use some work, as well. You seem to rely too strongly on the rhyme scheme, especially in S4 where the second line has been gutted just make it rhyme. Rather than focus on the rhyme, focus on what you are trying to say. For that matter, what are you trying to say? You're telling me a lot of things, but poetry is all about experience. How can you make your reader feel what you are talking about? Keep in mind that you can use poetic devices such as metaphors, rhythm, sound devices, and more specific diction (which isn't a poetic device, but whatever!) to give your poem more life.

Also, I'm not sure about the use of "sakura". Why not just use the English "cherry blossom"? You may loose people by your strange trip into Japanese. If it had more of a significance in the poem (for example, if the poem had a root in Japanese culture, or in a Japanese tradition) it would make more sense, but as it is, it's too random.

I hope this helps! If you have any questions feel free to PM me.