Read this in the 80's in a compilation of military Science Fiction short stories. The author/speaker is a human time traveller who has gone back in time and become a mercenary at a time when swords and pikes are the weapons. The time traveller's unit gets wiped out and while looking at the body of his buddy realizes the buddy was an alien (because of the green blood). there is a line about where he says you never told me you were (type of alien) and I never told you I was from the future.
This is "Saul's Death" by Joe Haldeman.
Saul's vitals were not human, but familiar.
He never told me he was from another world:
I never told him I was from his future.