Me and My Substitute

This story's pairing: the ex's unattainable ideal x the kept substitute

*This is a trope I've been thinking about for ages

*It's a short story

*With this trope, keeping things squeaky clean down there is out of the question

A simple blurb:

Their young love was broken up by their families. They kept seeing each other in secret for three or four years, but eventually they still broke up. When Fang Yuan heard that his ex was keeping someone who was supposedly his true love, he impulsively returned to the country, only to find that his ex's new lover looked remarkably like him...

(Contains scenes with both partners taking the lead)

(If you absolutely have to assign top and bottom, the substitute is the top and the ideal is the bottom)

(When two people who look alike fall in love, they always get mistaken for siblings, which brings its own troubles)

(Read with caution)

Premise: