She must be a couple of Sirius, Snape or Harry minimum.
To be completely honest with you, thank you for including the "Contro" tag, because this is controversial. While I thought you did a good job depicting Sirius' obsession, I do think he takes it too far as well. It did bring to mind an interesting idea though: how would your Sirius (the one as you've written him here) fare in a longer fic centered on the Ron/Hermione dynamic? It would be an interesting read, certainly, if you chose to expand upon what you've written here.
On a technical note, you seem to have a love affair with the comma. For example, these two sentences:
She caught his eye at the age of fourteen, young and still, for the most part, pre-pubescent. His attraction, at first, had been nothing physical.
And this one:
The idea came to him in a flash, he may have lost her heart, but he might still get to sample that delectable body.
As a suggestion, it might read more smoothly with dashes or semicolons in some places throughout your story. The way you have it now, it's heavily comma-spliced. This results in the feel of numerous run-on sentences.
Overall, though, I thank you for sharing the piece. Happy writing to you!