If you are at a party where many people suddenly encounter such a situation when someone starts to flirt with your man, you should immediately note your territory and keep no one to its borders.
No female in the world should even look at what is rightfully yours.
And if a man actively participates in this game with obvious signs of sympathy, then to whom, how not to show him that you are not very upset if he decides to leave you. But at the same time, you need to competently show your opponent that you do not even think that she can win.
Every time you meet her look, show all your nobility and endurance. And it will be better if, in the course of their lively conversation, you come to your man and take your hand, thereby showing the potential difference that they do not have such closeness as you. Try to wedge in the conversation and, if the topic is familiar enough for you, you can even argue a little with this lady, so as not to give the opportunity to be in a winning situation. Of course, you can argue only if you are sure of your rightness and can prove it by facts.
And it’s very important, never show other women’s women that your relationship can have disagreements.