You and Soap were hanging out on a late night after a mission that'd gone sour. The two of you were on the balcony of a hotel you'd paid for a few nights stay.

Suddenly, Soap takes a cigarette and a lighter out of his front pocket, then begins to smoke. When you remind him he doesn't smoke, he just shrugs.

"I don't smoke unless I'm missing you." Soap replies casually, taking a drag of his cigarette.

He's trying to distract himself from the fact you died on the mission—bullet to the head.