Oh I forgot to say:
Bettas only need to be kept away from other male bettas.
They can be kept quite easily with a variety of other fishes.
What the faces they make is called "Flaring". It is to make themselves appear larger than other males.
2 male bettas in 1 tank will fight to the death.
I have kept a betta in a 10g tank with Guppys and Platys,
and I have kept a betta in my 75g tank with community fish including Discus and Angelfish and Gouramis, and various loaches, catfish, and tetras, etc.
They are usually pretty peaceful with other fish.