What is the ruling on someone who causes trouble between an engaged couple so that he will call it off and she can snag him?
Question

                There is a woman who caused trouble between two people who were about to get married. She had intervened to resolve a problem between them, but she transmitted bad talk between them, saying that each of them had said bad things about the other. So they split up and there was a trade of insults and bad talk between them because of the words that had been falsely transmitted between them.

Then the young man went and proposed to the girl who had caused trouble between him and the first girl whom he had wanted to marry.

What is the ruling before Allah? Will there come a day when this man will realise that he unfairly mistreated the first girl or not?
Praise be to Allah.
      Firstly: 

    Causing trouble between Muslims is a major sin that corrupts intentions in 
    people’s hearts, spoils relationships between people, and spreads mischief 
    in the land. 
It 
    says in al-Mawsoo‘ah al-Fiqhiyyah (5/291): 
It 
    is prohibited to cause trouble and spoil relationships among Muslims, for 
    two reasons:

    1.in order to 
    preserve unity among the Muslims

    2.out of respect for 
    their dignity, because Allah, may He be exalted, says (interpretation of the 
    meaning): “And 
    hold fast, all of you together, to the Rope of Allah (i.e. this Qur’an), and 
    be not divided among yourselves” 
    [Aal ‘Imraan 3:103]. 

    Hence reconciling between people is one of the best of good deeds, and 
    causing division among people is one of the gravest of major sins, as the 
    Prophet (blessings and peace of Allah be upon him) said: “Shall I not tell 
    you of something that is better than fasting, prayer and giving charity? ” 
    They said: Yes indeed. He said: “Reconciling between people, for causing 
    division among people is the ‘shaver’ (that shaves one of religious 
    commitment).”

    Narrated by at-Tirmidhi (2509); classed as saheeh by al-Albaani in Saheeh 
    al-Jaami‘ (2595). 

    Hence the Messenger (blessings and peace of Allah be upon him) forbade 
    seeking out the faults of the Muslims, and he forbade backbiting, malicious 
    gossip, suspicion, mutual hatred, mutual envy and everything that may lead 
    to causing trouble among Muslims. End quote. 

    This prohibition is emphasised if causing trouble between people is done to 
    spoil that which could have been the means of bringing them together, 
    instilling love between them and uniting them, such as marriage. 

    Secondly: 

    Causing trouble between people usually involves telling lies, backbiting, 
    malicious gossip and slander, all of which are major sins. Please see the 
    answers to questions no. 23328, 
    101776 and 99554 for information on the negative 
    impact of these blameworthy characteristics and how to repent from them. 

    Thirdly: 
It 
    is haraam for a Muslim woman to cause trouble between a man and his fiancée 
    so that she may snag him for herself, for this comes under the heading of 
    bad conduct and blameworthy characteristics. Al-Bukhaari (6601) and Muslim 
    (1408) narrated that Abu Hurayrah (may Allah be pleased with him) said: The 
    Prophet (blessings and peace of Allah be upon him) said: “A man should not 
    propose marriage to a woman to whom his brother has already proposed and he 
    should not outbid his brother. A man should not marry a woman if he is 
    already married to her paternal aunt or maternal aunt. A woman should not 
    ask for her sister to be divorced so as to deprive her of what is rightfully 
    hers and so that she may be married in her stead; rather she will have what 
    Allah has decreed for her.” 

    An-Nawawi (may Allah have mercy on him) said: 

    What this hadith means is that it is prohibited for a non-mahram woman to 
    ask a man to divorce his wife and marry her instead, so that she gains the 
    maintenance, kind treatment, intimacy and so on that belonged to the 
    divorced woman. 

    End quote from Sharh Saheeh Muslim (9/193) 

    Al-Haafiz (may Allah have mercy on him) said: 

    This is quoted as evidence for the prohibition on a woman proposing to a man 
    who has already proposed to another woman. This hadith makes the ruling 
    concerning men the same as the ruling concerning women with regard to 
    proposing marriage. The scenario is: a woman proposes to a man, and he 
    responds to that proposal, then another woman comes and encourages him to 
    marry her, and tries to make him lose interest in the one who came before 
    her, whom he has already agreed to marry.

    End quote from Fath al-Baari (9/200) 

    Fourthly: 

    The issue does not have to do with whether all the parties involved in this 
    issue know what is happening or not, because worldly matters may be hidden. 
    But on the Day when all secrets will be exposed before the Lord of the 
    Worlds, and what was hidden in people’s hearts becomes manifest, what answer 
    will those who caused trouble and spread malicious gossip have before 
    Allah? 

    What the woman who has done this must do is hasten to repent, and part of 
    complete repentance is putting right that which she has spoiled and 
    admitting to each party what she said about the other, so that they will 
    understand the situation, then if they want to they can get back together 
    and go ahead with their marriage, or if they want to they can remain as they 
    are now. 
If 
    it is too difficult to state what really happened, then that can be done by 
    way of hinting or via a third party, striving to set things straight and 
    explain what really happened. 

    Please see also the answers to questions no. 14092 
    and 178714 

    And Allah knows best.