While this is a beautiful story, I find the punctuation (or lack of it) really distracting. Short sentences and commas are your friends; don't abuse "and" as a linking word. And try not to overuse the short poetic description sentence format because a sentence without a verb in it doesn't look good - you can do it sometimes but not all the time.

Sorry for the Grammar Nazi-ism, it comes out in gushes sometimes. Hope you can use these comments as stepping stones for improvement :)

I really liked the story though. Cass's desire for Dean is so heartwrenching, and the efficiency with which they live their lives, the sadness of it, really comes through. Your imagery is very vivid, and your descriptions are truly beautiful. :)