Looks like a male to me, at least from the pics. It still looks kinda young though, but I may be wrong. It's kinda easier to tell when they're together because the females are usually chunkier, and the dorsal fin on the male seems higher and has a more prominent blue line, at least in my experience.
If you still have the others I would put them all back together again, and just remove the others once a pair forms, and at the least aggression will be spread out during the bonding process.
If you don't, I guess the best thing to do, if your purpose is to attempt to eventually breed them, is to put them back together in a neutral tank thats densely planted and do the observation, trial and error route.
Auranti's are aggressive to conspecifics by nature and most of the time after battling it out for a while will eventually chill out, with the battles becoming less frequent if it is a true pair. There's no real scientific documentation that I know of regarding this, so in the end most of us learn from our mistakes and base a hypothesis off of others experience, until there's some consistency. Unfortunately one of the few things that are fairly consistent about everyones experience with auranti's is that they are nasty to each other. Good luck and let us know how it works out for you.