If you don't provide all of the data you can on an aquarium, you make adequate answering impossible.

In a sense, keeping a schooling fish by itself is cruel. Of course if you get schools of those fish and put them in a 10-gallon, in time that may be cruel too.

Your Betta may be keeping to himself because he knows it could be only a matter of time before his fins get butchered. Bettas are usually not a good idea with guppies. Barbs virtually never are. Those last two aren't with each other either.

Did you do a little book browsing or Googling of Guppylog or the Net for guppies and barbs or guppies and Bettas?

Putting incompatible fish together is a rookie mistake. You should be growing beyond that level. You certainly have heard people suggest that one should never buy a new fish until that fish has been checked out for physical needs, behavior, routine care, food, social needs and eventual size. :)

By the way, if you took the barbs away, the male Betta might be ok with the guppies. (He will "love" the fry.) Then again, maybe not. When you say that you have never, ever seem the male chase a guppy, have you watched him 24/7? ;)

A last point which is really administrivia: please answer a comment after the statement. If you answer just any place, the flow of the thread gets pretty strange, people get bored and go away.