So sory to read about the whole situation. Your heart must be aching terribly - I hope I never have to make a decision like that. My friend had to, though, when her male akita turned on her female akita and nearly killed her (after living together for many years!) My friend also made the choice you did and immediately put her dog down, not wanting to risk his aggression worsening.
As many have said, we weren't there in your shoes.
To me, it seems like you did try, you did work with a behaviorist - and you made a sane and mature decision based on the situation. I hope Charlie heals quickly. Prayers & light coming your way ---