How should I stop my best-friend if she is dating two men simultaneously?

There really is only one thing that you should do if your best friend is dating two men at the same time. This is to talk to your friend. You should never go behind her back and talk to the two men even if they are friends of yours.

It is really none of your business. If you best friend is dating two people at the same time, it may be because they are in open relationships where they have agreed to date more than one person.

However, if it is obvious that she is really just wanting to date two people, then you should sit her down and discuss the problems with that. You should explain that doing this could cause both of the men to leave her if they found out.