I've tried to give my betta some friends and he seems to not like it AT ALL!!!

I bought some neon tetras, and I heard that they liked to live in schools so I bought a few. I put them in his tank and then watched them for a while. I ran out to the store and my betta had bit the back fins off one of them and it appeared at somehow removed the belly/stomach area from the tetra. I also tried to let him look at a female betta through the tank for a while and he constantly puffed up at her and was violent acting. Is there ANY other fish or inhabitors that i could try out or should I cut my losses on a roommate for my lil guy?