TRISTAN: You are very odd, you know that?
RORY: Thank you.
TRISTAN: You’re welcome. [he kisses her. Rory pulls away crying] I’m sorry, what did I do? Did I bite your lip or something?
RORY: No, it’s not you. It’s just – I have to go. [runs out crying.]
It’s notable that Rory said “thank you” to Dean after he first kissed her, and now she says “thank you” just before Tristan kisses her. It is being kissed by Tristan which reminds Rory of her feelings for Dean, and this is what opens the floodgates so that she is ready to cry and mourn for their relationship.