However, in the process of ironing out the deal; to allow you to attack your 'partner' but only in order to reach the 3rd party 'victim' to kill him, the cad dishonourably attacked you.
.....I don't think it was a practical suggestion of terms, but I wouldn't have called it dishonorable. It just wouldn't work because we'd probably have to attack each other in order to take the other player out.
Your point of argument is simply about nuance not essence.