Look no further! It's not a problem with you, it's a problem with SSH client. The issue is that your private key file is missing the trailing newline and ssh just can't understand that file thinking that it's been encrypted with a passprhase -- what a dork!
your debug output would be like this:
debug1: read_passphrase: can't open /dev/tty: No such device or address debug2: no passphrase given, try next key