The act doesn't end on the sidewalk. Simon takes it with him in the car, in the restaurant, ramping up the humor and the charm to conceal his true emotions. He makes a show of enjoying the food despite how uncomfortable he feels. The more doubtful Sarah Jane looks, the more he performs, hoping she'll be charmed by his smile and his jokes not to worry about him anymore. He's secretly relieved when they return to her house. It means he can stop acting soon. He can slip away from her in the bar and be by himself and breathe that fake breath he breathes while he lets him feel all the things he's suppressed tonight.