You may not have any problems now, but they are aggressive. The betta splendens that we buy in the store are not peaceful enough to live together (unless in carefully monitored female sororities). There are other species of bettas that can live together, male and female, but these are not the type that are sold in pet stores. Their behavior can change at an moment, and their instinct is to be territorial and aggressive. By putting them together, even if they don't fight, they will be incredibly stressed out, with lower immune systems, and most likely will succumb to illness.
You could consider house a betta and a snail, fresh water shrimp, or, if your tank is big enough, other community fish.
How big is your tank?