i really wouldnt put a male & female in the same tank no matter what size it was unless it was divided!!
males prefer to be alone, females can be kept as singles or in groups of 6 or more to minimize bullying.
if you want a female in a community steer clear of fish with bright and/or flowing finns like guppies as they she may mistake it for another betta. Avoid fin nippers like neons.
Rasporas, platies & mollies are ideal as are bottom dwellers like corydoras, these are best in groups of 5/6 .