I am fairly new to cichlids, but if it were me, I'd put him in the 10 gallon by himself, let him settle in for a while, then maybe add one slow moving, placid fish (maybe a mollie or platy?) in case he wants company. One that won't be nippy or try to boss him around. Just a very mellow, sweet fish that won't intimidate him. If this stresses him, then maybe he just needs to be kept by himself, or maybe just with a couple of cories for bottom cleaning would be enough. I'd feel sorry for the little guy if he were mine! I know it can't be fun for him to be living in fear.