Agree with Curiosity, With Betta Fish the rule is usually to give them their own space (males). There is a big spectrum with their tolerance, and aggression levels, and ideally if you have them in a tank with other Anabantoids, or any other fish (Gourami's in your case) then you should have a back up plan. The issue is that they may seem to be living happily at the moment, but that could change. If so, would you be in a position to separate them? (do you have another tank if things get out of hand)?
You don't state the size of your tank, is it planted? Cycled? Which type of Gourami's do you have? are they male? female? both??? How long have they been sharing a tank. Betta's can get along with certain other fish/critters in a community tank, but it really depends on the individual, if it does not work out the consequences can be very tough for you and the fish.