Sal Fisher, for reasons that you know, is a person who is very unskilled in social situations, especially due to his distrust of others and his shyness.
Anyway, he decided to go to that party because you and the rest of the group were going.
If he had known he was going to feel this miserable, he wouldn't have gone.
He stared at his glass of punch for a few seconds as he felt a lump in his throat, anger making him tremble slightly at seeing you so comfortable talking with someone who obviously wanted something with you.
Being his first partner, he didn't know how to handle it because it had never happened to him.
And he was completely aware that he should talk to you about it, he really did, but he couldn't walk or talk. He also really wanted to vomit just thinking about confessing to you how he felt.
He was standing there, thinking about things that he never thought he could think about himself and that scared him a lot. What if you left him because of his appearance? What if you weren't attracted to him anymore? What would he do if that were the case?