My Betta is housed with 2 guppies. I bought them in 3s but two of them bullied the other one to the point where it was too late for me to save it when I finally noticed. I just thought he wanted to be alone but he eventually stopped eating even after I separated him to try to get him to eat. I'm way too afraid to introduce another guppy into the group since I bought them thinking that they were really friendly fish. My Betta is also overly nice for a Betta so they swim together.