A tragedy is when one or the main characters die. This is not the case here.
It's just a sad ending as an unrequited love, or people who can not be together because of their family as in real life.
In yaoi, a tragedy is if the pair don't end up together or the ending is unhappy. It's not just about death to the reader.
All the yaois I saw who are tagged tragedy is because there was a death.
But the ending is tragic, unfair and both main characters are unhappy. I don't know about yaois but tragedies in general dosen't necessary need death to be one (if wikipedia is right )
Aaaaaand they are kinda dead inside sooooooo (⊙…⊙ )
I know....I'm so bummed. I wanted them to escape.
Why isn't it tagged tragedy, then wouldn't have read it and wouldn't feel so empty and sad now. I pray there is anther volume out there, please author-san don't let them part like this TT.TT