Yeah you can't put the male with the females because it would stress them out and the females might actually die if he tries mating with them and "beats them up" too much.

Goldfish are partial to colder waters but can survive in warmer waters as well. And of course male bettas are aggressive but only toward other aggressive fish. My manager while I was at PetCo had a huge tank full of a wide hodgepodge of fish -- "sharks", one male betta, goldfish, mollies, tetras, plecostomus (did I even spell that right) and all sorts of other stuff and they all lived in conjunction of one another. Now that isn't smart of course but it was just odd that it worked out