The two lovebirds out for date night may adore your fine-tuned stories. They may think you're the most hilarious bartender ever. They may even invite you to pull up a bar stool. Do. Not. Do it. Three is a crowd.
Provide the best service possible to all your guests in the restaurant, and then, if that offer still stands when your shift is over, change out of uniform, let your hair down, and with care not to overstay your welcome, join in for a drink. Otherwise, let people enjoy their night out without adding yourself to the reservation.