I would say that if you like to have a male betta, then it would be best to separate him in a smaller tank, as long as it is sufficient swimming space with proper filtration and heating (as usual). It also doesn't necessarily mean that he should be kept alone. If the would-be tank is give enough, then you would be able to keep shrimps (ghosts), ADFs, Snails, Neons (a small school in a 10G with a betta), etc (Compatibility issues depend on the individual betta).