When to separate the male and female after mating?
As soon as spawning has finished she should be removed. The male will chase the female and kill her otherwise.
Do you mean baby mice? Baby female/male mice can start mating at about 6 weeks, and you are safe to separate them from there mother at 4 weeks, so the ideal time to separate them is about 5 weeks. If you mean 'when should you separate adult mice female/male' You should always have them separate unless you want them to mate.
Why would a male leopard gecko show aggression toward its owner and toward its female companion other than normal mating?
In some species the male spider seems to sacrifice itself after mating. In some species the female spider is very likely to try to catch and eat the male after mating. In many species there are special adaptations that help the male escape from the female after mating. In some species the males are tolerated and may live in little webs near to and perhaps attached to the web of the female.