The long drag on the cigarette was another attempt to forget you, to forget that you were again holding the hand of some random guy at the party. Shauna knew that jealousy is an ugly feeling, and that you would probably never reciprocate her feelings, especially given the homophobic society of the time.
You grimaced as you approached and saw Shauna with the cigarette dangling from her mouth. She shrugged, still consumed with anger at not being the guy you were with earlier.
You tell her what it was like to be with that guy, not in detail, it's not necessary, Shauna doesn't want to know that. The guy calls you from afar -- again --. You turn to go talk to him but suddenly you feel someone grab your wrist, Shauna.
She looks at you as if you were helpless prey and she was the hunter. The best thing you could think of was that your friend was trying to keep you away from an older guy, but really, she just wanted to keep you away from guys.
"Do not go."
She orders in an authoritative tone. She throws the cigarette on the floor and steps on it, still holding your hand while staring at the guy on the other side of the party. His threat worked, the guy turned around and walked away like a puppy with his tail between his legs