well the usual advice,
you need to see a lawyer who has a criminal practice.
Having lived in Plymouth (Stoke), come on Marine, you know you are not meant to brawl with anyone except the commandos....and yes a conviction of this sort WILL interfer with re enlistment. Jesus, how old are you ? You first stint in the Marines should have taught you enough discipline to keep your hands to yourself in public
The difficulty is, that you broke the other man's jaw, and only got a few cat scratches yourself. You need a lawyer to explain that one.
and Good Luck - I agree it could have been a mistake.
PP