I like it because it shows how affected she was by the kiss by acting nervous when she sees him.

When she sees him with Jen, she has a look like why is he kissing her instead of me. Before, it was hypothetical and she wasn't taking him seriously, but when she sees him kissing Jen, she acts like someone who's being cheated on. Jen tells Pacey that she overreacted and points out he overreacted to Dawson