Restraint.

"Maybe we should just go home." You reach up to cup her chin in your hand, and she rubs her cheek against your palm.
"Why...are you such a good guy, James? It just makes me want you more!" Your palm moistens from gentle tears.
"I'm not a good guy, Tara. Good guys don't make out with their son's girlfriends on the hood of a car."
"You're a better guy than you think, James..." she climbs off the hood, and you swing your legs around, pulling her into a hug. You indulge this fantasy of a road not taken for one more brief moment, then climb back into the car to head home.