Causing an Engagement to be Called Off
Question

                I am a young man who was in love with a girl who was a friend of mine in University. Allah knows that my intentions towards her were sincere and that I was sincere in my relationship with her and I wanted her to be my wife, and I used to advise her with regard to that which is pleasing to Allah. I discovered recently that she had made the mistake of having haram (impermissible) relationships, such as talking to a number of other young men, and that she used to tell me lies and she betrayed me. Sometime after that I wanted to be close to her so that I could remind her of her Lord, bring her closer to Allah and keep her away from the wrong path that she was following. 

Long days passed and she got to know a young man without me knowing and she gradually grew apart from me until I found out that the young man had proposed to her and she was happy with him, and she had forsaken me and everything because of him, and that she had been lying to me when she said she loved me. I could not control myself and the Shaytaan took advantage of my anger and weakness; he made me speak about her past in front of this young man so that I could get my own back on her and cause estrangement between her and him. That indeed happened and the engagement did not go ahead. Now I feel that I have committed a grievous sin because I spoke about her and her past. I did not add anything to that; I only spoke of something that she had actually done.

Now I am asking Allah to accept my repentance and forgive me for the wrong I have done her, and I always make du‘a (supplication) for her in my prayers. Will Allah accept my repentance? What should I do? Please advise me, may Allah reward you with good.
Praise be to Allah.
    Firstly: 

    Any relationship between a young man and a 
    girl who is not his mahram (close relative whom he is forbidden to marry 
    forever) is a haram (unlawful) relationship, even if he claims that he is 
    sincere towards her or that he wants her to be his wife, and even if he is 
    calling her and advising her, or so he says, to be more religiously 
    committed. He does not have the slightest duty of guardianship or right over 
    her. 

    Abu Nu‘aym narrated in al-Hilyah that 
    Maymoon ibn Mahraan said: There are three things to which you should never 
    expose yourself: do not enter upon the ruler, even if you say, ‘I want to 
    tell him to obey Allah’; do not enter upon a woman, even if you say ‘I want 
    to teach her the Book of Allah’. And do not give your ear to anyone who 
    follows his whims and desires because you do not know, something of what he 
    says may take root in your heart. 

    Shaykh al-Islam (may Allah have mercy on 
    him) said: 

    Falling in love with a non-mahram woman 
    leads to evil consequences the extent of which only the Lord of mankind 
    knows; it is one of the diseases that corrupt a person’s religious 
    commitment, then it corrupts his mind, and then his body.

    End quote from Majmoo‘ al-Fataawa. 

    See also the answer to question no. 
    
    82941

    We praise Allah, may He be exalted, for 
    accepting your repentance from this great calamity and evil. 

    Secondly: 

    Undoubtedly when you got angry for your 
    own sake and wanted to take revenge on this girl, then disclosed her secret 
    and strove to spoil her engagement, even if that was by speaking about 
    something that had actually happened, by doing that you made several 
    mistakes; in fact you committed a number of haram actions. You disclosed the 
    secret of the girl, when Allah has commanded us to conceal the secrets of 
    the believers and warned us against exposing them, transgressing against 
    their privacy and highlighting their faults. You engaged in backbiting about 
    her, even if you said things that were true about her. This is the essence 
    of backbiting, which Allah has forbidden. Then you tried to cause trouble 
    for her, and you managed to do that. There is no strength and no power 
    except with Allah. 

    The Prophet (blessings and peace of Allah 
    be upon him) defined backbiting as “When you say about your brother 
    something that he dislikes.” It was said to him: What if what I say about my 
    brother is true? He said: “If it is true then you have backbitten about him 
    and if it is not true then you have told a grave lie about him.” [Muslim] 

    Ibn Hajar al-Haytami (may Allah have mercy 
    on him) said: 

    Al-Qurtubi and others narrated that there 
    was consensus that backbiting is a major sin. End quote. Az-Zawaajir

    Thirdly: 

    If you have repented sincerely, then there 
    is the hope that Allah, may He be glorified and exalted, will accept your 
    repentance and enable you to make your repentance sincere, and will help you 
    to mend your ways and keep you steadfast in the future. 

    See also the answer to question no.
    
    13990 

    You have done well to admit your sin and 
    acknowledge that you did her wrong. This is the first step on the road to 
    repentance. What you must do now is everything you can to put right what you 
    spoiled. First and foremost you should pray for forgiveness for her and ask 
    Allah to accept her repentance and to set her affairs straight. 

    Fourthly: 

    You have to try hard to speak highly of 
    her in the places where you spoke ill of her, as much as you are able to do 
    so, and to the extent that is appropriate when speaking of a woman who is 
    not your mahram, even if that means saying that you were lying when you said 
    the things that you said before, or explaining that it was your anger that 
    made you say that. 

    Fifthly: 

    You have to seek her forgiveness by asking 
    her to forgive you and acknowledging that you did her wrong, and that you 
    are trying hard to correct your mistakes, because one of the conditions of 
    repentance being valid is that if it has to do with the rights of another 
    person, it is essential to ask for their pardon. This applies if speaking to 
    her frankly will be beneficial in this case; otherwise it is sufficient for 
    you to pray for forgiveness for her and to try to put right what you have 
    done wrong, as stated above. 

    See also the answer to question no.
    
    6308 

    And Allah knows best.