So sorry for your loss.
Males and females can only be kept together when breeding and then only for a short time. They can be extremely aggressive towards one another and it sounds as though they attacked one another. I'm not too sure about your tetras but they may well have been killed as well.
Male Bettas aren't great community fish as they can be territorial and don't like sharing their tank with other fish.
P.S. Amunet, sorry but your answer came across as a bit harsh. The chances are the Op was given bad advice. I had the same problem when I first got into fishkeeping. I was told by my lfs that a male and females would be ok together.