This story is so cute, but saddening at the same time, as I can sense what will happen. You've come up with a perfect story. Yes, it's perfect :)
That said, I do have some critiques:
Ok, so I love the first sentence. However, what does "window feet first" mean? Did you mean something like "...he was climbing out of my bedroom window, feet first,...etc."? Is that what you mean? otherwise, I have no idea with a "window feet first" is :P
Ok, second sentence... how can the girl's hand be glued to the light switch(metaphorically) and than "blink"? Confusion!
Also, when I start reading, I feel no emotion behind the characters, as their speech and the way you describe their speech is a bit bland. Spice it up a bit, because I really like this story. Ah, I just want to feel the emotion of the characters!
With that said, I did warm up to the characters by the end of the first chapter. However, I really want to know the characters right off the bat, though that's only my opinion.
So, and impressive first chapter. Love it!
It's getting late, and if I had more time, I'd keep reading.
But bravo! Ah, this is very good. Very good indeed :)
Amazing job!
Keep writing!
---RbG