why did you separate them? is she injured?
if you separate them he will start all over again so i don't think it's a good idea at all. I would leave them to it, if you separate them i think it could get a lot worse when she returns. IMO it's best to leave it to them to sort it out, if one dies then so be it. Removing a fish for protection is delaying the inevitable i think, these are animals that have their own ways of sorting things out and that applies to male v male scraps to.