>>11412694
There is a story with a similar premise, where at the end the futa confesses that she intentionally got with MC's ex gf's because she was saving him for herself. The story has its own fair share of faults, but you may like it nonetheless.

Birthday Party [3 chapters, finished]:
>https://www.literotica.com/series/se/138871570
It also comes in audio version (so the story is promptly modified):
>https://www.literotica.com/series/se/493600637