Iubilantium te virginum
As Stephen left the KFC, he was thinking of the Rituale Romanum; This is the part of the commendation for a departing soul. Not that she were dying; but he knew at that moment that it was beginnning of the death of her memories.
Life has offered Stephen innumerous tempations of a conventional existance, this time he decided to plunge into the labyrinthine maze of self-doubt, self-examination and unhappiness that comes with letting go of her rather than carry on. As did his namesake in Joyce's Ulysses, Stephen had no intention of going back.
Would you give up what could be, for the sake of what is? She was very pretty, as lovely as the sun is bright. There was something special about her and then too, there was something special about them; but they had never delved into the 'us' part, they had always been he and she. Time might have changed all that. A couple of months and there wouldn't have been a he and she, but Stephen was not willing to take a chance. What could be is not as valuable as what is.
"You have to forgive me for this; we won't be meeting again". Little did she know that he had not given up on her; he just wanted to hold on to her.
PS: As you might have guessed, this is about Stephen parting with his girlfriend. He considers their relationship pristine; at the first blemish of a smear on their relationship, he decides to end it. He isn't thinking of the higher planes that relationship might have reached; he cherishes whatever they had between them and feels that giving it up was the best way to keep it immaculate.