Seeing Sasha hug Vaughn instead of him kind of... hurt. A lot.
It wasn't the act of hugging Vaughn that elicited these feelings of hurt. No, it was something else. Something that went much deeper than misplaced jealousy over Sasha readily choosing to place her arms around his best friend's admittedly more-in-shape body - okay, maybe jealousy played a role in the formation of these new-found feelings. But it was tiny. Minuscule. At least in comparison to the biggest reason...
It was plainly obvious that he went in for a hug, and plainly obvious that her swift dismissal of his affections bothered him much more than he let on. The subsequent exchange between him and Sasha made it difficult not to characterize the whole thing as tense and awkward, brimming with unresolved issues. His woeful attempts to conceal the hurt and smooth things over didn't help at all. Going for detached and cocky yielded bumbling and cheesy. The words that appropriately conveyed nonchalance gave way to a stuttering, convoluted mess. He wasted precious seconds putting on a cool facade (and failing) as opposed to saying what needed to be said.
He could've told her what he really meant. Told her that people make mistakes. Point at himself. Exhibit A. Make her laugh and make her forgive him.
What could've been a heartwarming reunion between friends turned out to be... Not that. Less than that. It was so clear to him now. The opportunity to become "more than friends" ended where his decisions began.
And realizing it was all his fault hurt the most.