a cross-post, in the event my community entry is not moderator proof at little_details

Nobody wants to cross paths with their old high school flames, at least that's what I've heard. I think there's an exception to that rule and this doesn't apply to people who might've been heartbroken over the split between their "first loves". So, the story starts more than twenty years after the relationship, and considering that the two love birds in question were adolescents, they've changed dramatically in their appearance so much so that neither one could be expected to recognize the other. Nevertheless, by happenstance, the two cross paths.

The heartbroken of the two thinks that he recognizes her, yet he doesn't acknowledge nor seek affirmation that she is her by simply asking "do I know you from somewhere". It is really moments after this encounter that the protagonist conflict is revealed. The backstory, however, must convey sexual frustration for this character because it was a result of his unfaithfulness to his gf that causes the break-up way back when. Even though he's been in and out of very few relationships since then, because nobody seems to meet his expectations, he won't even try to pursue anything more meaningful than casual sex.

On the other hand, the catalyst of his lost love's menopausal behavior upon learning that her high school sweetheart is still hung over her, gives credence to the idea that their encounter at the beginning of the movie was not coincidental. How do I convey a backstory for the protagonist as someone who's transgression transformed him to vow never to fall out of love with the girl whom he's out to prove was not a figment of his imagination after seeing her double twenty+ years later?