One thing missing from your post was a little more about the relationship between the two dogs in previous encounters; ie, did Max react to Romeo's aggression by lunging back at him, snarling and trying to bite him? Or did he try to run away and turn to fight only when cornered? Generally, the only time a fight between dogs will end in severe injury or death is if both dogs are dominant/aggressive - ie, neither dog tries to escape or submit. If one's trying to get away or submitting, a normal, sane dog will let it go. Even a dog-aggressive dog will let it go. If, as I suspect, Max wasn't aggressive except in self-defense, Romeo's killing of him can't be dismissed as a sad outcome of a natural power struggle.
There's dog-aggression, and then there's a dog that will kill another dog. This is not normal canine behavior. It is possible that some of the problem is his early separation from the litter, as those first weeks are supposedly the time when they learn a great deal about appropriate canine interaction and bite inhibition. Whatever the root of the problem, you now own a very strong male dog in the prime of life who has been practising attacking another dog for two years and has finally completed the exercise successfully. Romeo is extremely dangerous to other dogs.
I believe, based on your postings here, that you're unable to handle Romeo so he will not get another opportunity to attack and kill another dog. Life isn't perfect, and you just got unlucky in having a very difficult dog during a time period in your life when you need an easier dog. But based on his long-term behavior, the final lethal attack, the relative inexperience of everyone involved with dealing with a real problem dog, and the fact that your circumstances are such that he can't live with you, I would say that it's your responsibility to have him put to sleep. I would say the same if he was a Lab or a Newfoundland. There are plenty of dogs, plenty of pit bulls, who would not have done this. I think you have to love Romeo, cherish your memories, and let him go before he can cause more grief and death. It's a horrible situation and I'm very sorry for everyone involved.