A Betta ability to to co-exist with any type of other freshwater fish depends in its persinality and how the tank is setup, in a larger, heavily planted tank you are more likely to encounter less problems concerning negative Betta compatibility. There are a range if typically general tank mates for any male Betta Splendens. Most would be along the lines of Corydoras, neons, and most rasboras. It would be helpful to know this vital information to depict the right tank mates
How large is your tank?
How much cover is there?
Pictures?
How passing is your Betta?
Does he flare very often?
Type of substrate?
PH, and hardness?