Just to add another two cents worth to my previous two cents (wow the cents are piling up), I have had a similar experience where I was actually able to keep two male bettas together in the same tank with no problems (started out as an accident - one betta jumped from one tank into the other - but since they got along fine I left them together). Not to say that I'd recommend trying this, just to reiterate that it really depends on the fish's personality as to who and what they are going to get along well with. I actually brought home a male gourami from Petsmart without realizing that typically they are not compatible with bettas. the gourami turned out to be suffering from what we think was damage to his labyrinth organ and gills from unstable oxygen in the tank water at the store... in any case the poor guy only lived about a week and a half but the betta actually stuck to his side and defended him from any other fish that came too close for the entire time he was in the tank, so go figure. It's definitely a lot easier when you have more than one tank where you can shuffle fish around if they are not getting along