Half gallon is too small for a betta. They advertise all that junk at the pet stores 'made for bettas' - don't listen to them, it's all rubbish. Would you like to be locked in your closet to live for the rest of your life?
Okay, if your husband said go get more, I'd say get a 10 gallon tank (they're cheap anyhow) and divide it. Betta fish aren't called fighting fish for nothing, do NOT stick two males together, they will fight, tear each other's fins to shreds, and likely kill each other. Likewise, females are not really much friendlier. Do not stick a male and a female in the same tank and think it will work (do not listen to the salesman at the fish store if he tells you this is okay! They are lying through their teeth!). There is no love at first sight with bettas. There is a lot of posturing, flaring and fin-ripping. They are 1 fish, 1 tank kinds of creatures. The way around this, I have found, is to take 10 gallon tanks, and put a divider (or two) in them and one betta goes in each section, while still giving the betta enough space to swim(10 gallon tank divided in two is 5 gallons per fish, divided in three is 3.3 gallons per fish). This way they can see each other and you will get to watch them flare and interact, without any of the nasty side effects of fish killing each other.
You can buy dividers at a petstore, but I find these are pretty poor excuses for dividers (the holes are tiny and don't allow good flow, the divider often will kink and not lay flat, and they form a poor seal around the edges and sometimes fish can slip through) and they are expensive! There is a cheap alternative instead, and that is to make your own tank divider - don't worry, it's really easy, and cheap!
That should have all the info you need on making dividers.
If you get a 10 gallon tank, grab yourself a 50 watt heater, and that will work for the whole tank. Betta fish are tropical, and like warm water. You'll find a warm betta is a happy betta, and they are much more active when they're warm.
Bettas and other fish. Eh, this is a topic of much debate. Bettas are aggressive fish, as has already been said. This is not restricted to their own species. If another fish has long fins or bright colors (aka even vaguely resembles a betta) the betta fish is likely to attack it. Guppies, gouramis, angelfish, chiclids, goldfish etc are all a big no-no. There are stories out there of people keeping their betta with fish that are normally considered a horrible match and the fish not fighting. Personally, I wouldn't try it. These are rare exceptions to the rule and they were lucky (and probably a bit fool-hardy to try it in the first place). A lot of people like keeping bettas with Cory Cats (Corydoras Catfish), since they usually leave each other alone and get on well enough. If you go the route of getting Cory Cats, know that they are schooling fish, and you'll want at least four of them in the tank (10 gallon or more). If you go this route, the tank cannot be divided, as they will need the whole tank to roam, which means you can only have one betta in there.
You will find bettas are actually quite smart as far as the fish world goes, and they each have their own personality. This means sometimes a betta will get along with other fish.... sometimes they won't.