Here is the full list of all 31 STAY achievements.
Reach the final chapter with the highest emotional bonding
Reach the final chapter with the highest level of trust
End Quinn's journey with a feeling of Acceptance and Hope
Become the perfect soulmate and never leave Quinn
Cracking the final code
Memories shaped into bits and pieces
Dance with the ugliest partner
Play it cool
Bad hair day not allowed
Don't lose sight of the north
Never leave the magic circle
Hail to the chief
Board game solitaire
Guardians, feathers and the unknown
A life within a life within a life within...
A never-ending book which is not for Bastian
Don't leave during a time interval
Never kill the cat
Who are you, stranger?
And then there was light...
Stare at the full moonlight with Quinn
End Quinn's journey with a feeling of Bargaining
End Quinn's journey with a feeling of Anger
Back to square one
End Quinn's journey with a feeling of Isolation
End Quinn's journey with a feeling of Denial
End Quinn's journey with a feeling of Depression
Reveal all possible endings
Discover all possible items
Unveil all secret rooms
Collect all the other achievements