you are headed to disaster, 120g? those fish? allot find fish beating up each other a fun thing, I am not one. i have a jag tank, and jags only, in a 145. they are a mated pair, I have to put a divider in between spawns or male kill the female. your fish to small to sex ATM IMHO.
enjoy the cage fight, not my cup of tea.
I've had one for a few months in a big tank, and he's nothing but trouble. Just like you describe, relentless. He gets whipped, it's like it didn't happen an hour later--he's right back to trying to take over the tank. He has no respect for bigger/more dominant fish, he keeps half of a big tank empty for himself, the rest of the fish get the other half. He does it through pure persistence.