Absolutely! unless going to breed them, you shouldn't keep male/females together at all - the male will be too agressive towards her & may even end up killing her. Even when breeding, the female should only be introduced to him very slowly after he has built a bubble nest & after they have spawned & eggs have been laid, you have to remove the female because of his aggression towards her.
Female betta's can be kept together but this can depend on their personalities & space. Keeping 3-4 females is better than 2. I had 2 females betta's in a 10 gall. once & they nearly tore each apart (females can be just as aggressive as the male), so I had to separate them, later on I had 4 females in a 10 gall. & they were fine.