resolute (слэш)

Trying to push his panic back, Nick popped on his hazard lights, eyes flicking between Carisi and his mirror so he could try to find a break in traffic to open his door. Before the stream of cars broke, however, Carisi shakily turned back to the car, face set in a cold expression that Nick didn’t think he’d ever seen on the other detective before. He looked up at him, “You okay? I can take you back home if you’re still feeling sick.”
The vomit bag crinkled in his fist as he tightened it. Carisi shook his head, “No I’m o-, uh, I just need some fresh air.” He snagged his satchel from the passenger side floor, never looking Nick in the eye, “I’ll walk the rest of the way. You go on ahead. Sorry.” And with that he turned away, pushing the door closed and starting off on a brisk walk toward the courthouse.
What the fuck just happened?