If you offer someone heart full of love, don't expect that you will get the same. Joke of the nature is that smart, beautiful women involve with bad guys, who are not able to give love back, or they will give love to someone else, even that person is not woman of dreams. It looks like story is over when your beloved chose your competition, but not everybody will make peace with that solution. A woman scorned will say "it ain't over until is over", because her word is the last.
The last hanged woman in Great Britain was Ruth Ellis. She killed her lover David Blakely, after dramatic love story. He was abusing her, underestimate and humiliate, so she decided to kill him. She had cooperator, Desmond Cussen, man who was in love in her. He gave her pistol and drove her on the place of crime. Ruth got death penalty for crime passionnel. Sudden strong impulse prevailed so Ruth signed her death sentence because of discarded love.
When you are in situation to make comfort your best friend after her man broke her heart, you need objective way to find solution.
The worst you can say is next:
Take care your health, he is not worthy. She already knows that, and in this way you made patient from her.
I saw him with new girlfriend, she is beautiful. Ok, maybe she is sex bomb, but your friend is broken and she doesn't need kick for ego.
My cousin asked about you, dear. Leave your cousin or friend by side. Love is not candy, that you can buy another just like that.
I knew he is not for you. This is not time to make yourself wise.
Your friend is destroyed emotionally and mentally, and she can do many stupid things. Attack her rival, try suicide, cry in publicity, these are all side effects of breakup. She is a woman scorned and she will wish revenge.
If you wish to advise your friend, use cold mind. You can support her in her intentions, from far. So, yes you agree that bastard must suffer, but let the river flow and when things get cold , make a good plan. You can ruin him reputation by telling your friends about him, who is he and what he did. Some people will think that you are jealous, but there is always weak spot in chain, so maybe this loverboy lose respect of society, at least in the circle where he is so popular. Someone got disease from him, he was in brothel or so on. Such stories will always make seed of doubts.
Even this woman will be subject of judgement, because she did not accept defeat, try to imagine yourself in her skin. She had boyfriend and suddenly one girl stand on her place. If she was married, even worse, her children lost dad and they are mocked by their friends. Dad escaped with whore, that is really bad story. It is not nice when you shared life with someone and then he decide to go away, because he needs change. You want to kick him from your life and from your circle of friends, so then here will start war for mutual friends. Not everyone will stand by your side, because that husband was their friend too, they watched football together and now when she found whore things are complicated, but life is going on.
Ruth Ellis is drastic example how to make paycheck to man who left you. The real solution would be, make yourself happy. When he see that you shine and smile, he will may relief, but deep in the corner of his soul, he will regret what he did. Somehow, someday, life will punish him too. Maybe not in private life, but he could owe money or lose job, so that is also kind of karma.
When you bite around after lost love, you bite yourself indeed. Don't lose basic values, because anger is kind of poison, it spreads in all areas in your life.