Do not put another Betta in with him, male or female.
You don't say how big your tank is. I'll assume it's 10 gallons. You can add 3 Corydora catfish (must be kept in groups of 3 or more). They are amusing to watch, and I've never had a Betta mind being homed with them. They also clean up any uneaten food from the bottom of the tank, keeping it clean for you.
If your tank is only 5 gallons, you could add 2 Platies, but that's pushing it. I've had Platies and Bettas together lots of times, and they've always gotten along well.
Do not add any fish that have long flowing fins or tails (such as fancy Guppies). A Betta can mistake them for another Betta and attack.
If your tank is less than 5 gallons, you really shouldn't add any more fish. You could maybe add a few ghost shrimp or something. I don't keep snails in Betta tanks, I have heard horror stories of the Bettas eating the snails alive. I honestly don't know if they will bother shrimp or not, I've never kept them together.
These are my best suggestions from my own experience. Hope they help.