If there was such a thing as the Bad Luck, Old Chap award and it had a category for antiquity, I would definitely nominate -
Craterus
Serves Alexander with distinction,
Could have been the man to whom Alexander left his empire,
Falls under his horse and dies early in the Wars of the Successors (Diodorus XVIII.30).
Perdiccas
Serves Alexander loyally,
Forms an effective team with Hephaestion in India,
Is deserted by his friends after failing to clear a disused canal (a canal!) (Diodorus XVIII.33)
And is assassinated after failing - wait for it - to cross a river (Diodorus XVIII.36).
Sometimes, it’s just not meant to be.
The Second Achilles 