Unfortunately 99.9% of fish store employees could care less about the fish. It aggravates the crap out of me! Don't feel guilty, hopefully they'll end up going to good homes. You can divide the tank and put another male or female into the tank. You could even divide it three ways so each fish has 3Gs. You could also put 4 or 5 female bettas in called a female sorority and put the male in a separate tank. Males and females should never be in the same tank together unless you're breeding them or the tank is divided.
What type of female fish would you want to use it for to give birth in? If you're talking about female bettas, it doesn't work like that. You have to breed a pair separately and even that is risky. The male could kill the female or the female could kill the male.