The review by Andy is harsh. There's no need to be that hostile when you review somebody's work. He's old enough to know better. You've taken the trouble to put your thoughts and feelings down in writing and that should be respected.
We should keep in mind the age of a writer when we review. An 18 year-old is pretty young (though might not feel it!) and will still be developing a literary style. They shouldn't be judged by standards that apply to mature writers.
In terms of the poem's length: shorter is better. It makes the sentiments more intense. I wonder if you read much poetry? Read some good poetry, and see how the language is compressed, how strong images are used.
Enjoy your writing!