So the story starts with some bird in a cage that won't fly out of its cage even when the door is open. And I think person A has a relationship with another character while person B is in love. The relationship between person A and the other character fails and person B is happy. The whole story uses a metaphor that person A is the bird in the cage that won't fly out even when the door is open. I think it's a oneshot at the end of some manga but I can't find it anywhere. It might be a shounen-ai.
Thanks

Does anyone know what manga this is?

Okay! This one was driving me crazy because I knew I had read it but couldn't remember the title or mangaka to save my life... but I finally came across it again!

The oneshot title is The Loose Shackle and its chapter 4 from Mezame no Mori by Aoi Yuna.