Yeah, just two things really.
"I were" should be "I was". "You were my friend" is correct, it's a bit much to explain, if you wish to learn more about their uses, try googling "i was or were", that might come up with it.
The other thing isn't so bad, and I'm not entirely sure if its wrong, or just doesn't sound natural.
"But I can't let you kill more civilians"
Sounds better as
"But I can't let you kill any more civilians"
in American English, I think it's one word "anymore".