Pain and Insecurity;
When Nathaniel first saw Serena again, he realized that, since she left, he'd been living his life in a haze of pot smoke and the expensive alcohol Blair loved. This realization, while disconcerting, was not surprising. Her presence alone caused such an intense feeling of pain in his heart that he stumbled down the last few steps, his cheeks heating in an embarrassed blush. His eyes met hers, and he could swear he could feel the love oozing out of his eyes.
When she ignored him, his heart almost seized.
When Serena first saw Nate again, his shirt wasn't tucked in; his cheeks were bright red, from over-exertion, and pupils wide. He was either high or just had amazing sex; Serena couldn't determine which.
When their eyes met, sky blue crashing into ocean blue, she had to look away. His eyes held such a look of affection that, for once in her life, Serena Van der Woodsen felt insecure, as though she wasn't good enough, that she wasn't worth this boys love.
When Blair came in right behind him, dress riding a tad high, hair out of place, Serena had her answer. They'd just had sex.
She knew that look of affection wasn't meant for her, just remainders of the love he had for Blair.
Serena said the obligatory hellos and kissed everyone on the cheek, never once looking at Nate. She then took her leave, her tail between her legs.
She needed something to drink.