He asked her for money or a ticket to travel to meet her, then he did not go
Question

                I was in a relationship with a non-Muslim girl who lives in a different city. One time I wanted to visit her so we agreed on a date and I booked the plane ticket then one day before travelling, she decided that she did not want to see me at all, so I cancelled the trip and asked her to give me the value of the ticket which I did not use, because she was the reason why I lost that money, and she sent me the money in full. Now, after I have repented and I ask Allah to accept that repentance, do I have to return this money to her? Because basically I am the one that was in the wrong. Is it permissible for me to marry her if she is guided and embraces Islam?.
Praise be to Allah.
      Firstly: 

    We praise Allah for having blessed you with repentance and 
    turning away from that haraam action, and we ask Him to accept your 
    repentance from you and to make you steadfast in adhering to guidance and 
    the straight path. 

    You should know that the prohibition on zina, and the 
    prohibition on such illegitimate relationships, has to do with the rights of 
    Allah, may He be exalted, and it does not have to do with the rights of 
    people. It makes no difference whether the woman with whom zina is committed 
    is a Muslim or a kaafir, and it makes no difference whether she agreed to 
    that or even wanted it, or whether she was forced into it. All of it is zina 
    on the part of the one who does it and is haraam to him, even though some 
    kinds of haraam actions are more forbidden than others, and zina with some 
    women is worse than with others. But this is another matter which is not 
    what we are talking about here. 

    Beware of the way the Shaytaan deceives many Muslims and 
    makes them take lightly the matter of sinful relationships and even makes 
    them fall into zina and sins that cause a person’s doom, and they think that 
    if the woman is a kaafir, zina with her is less serious, and they may not 
    think that it is haraam zina. 

    Secondly: 

    This money that you got comes under the heading of consuming 
    people's wealth unlawfully. You did not have the right to travel to see her 
    in the first place, and if you had travelled you would not have any right to 
    get any money from her in return for your travel expenses. If you incurred 
    some material loss as a result of your travelling, or of not travelling in 
    this case, she is not responsible for any of that at all and it is not 
    permissible for you to take material compensation for what you lost. 

    What you have to do is return to her the money that she sent 
    to you, and explain to her that it is not permissible for you according to 
    your religion, and that the relationship that existed between you is also a 
    haraam relationship according to our religion. And you should explain to her 
    the meaning of repentance from haraam relationships with women. 

    Thirdly: 

    If this woman actually enters Islam willingly and it becomes 
    apparent to you that her case is genuine, then there is nothing wrong with 
    you marrying her, although we advise you to close the door to any attachment 
    to her and avoid waiting in the hope that she becomes Muslim or becomes 
    interested in you. You will find among the chaste Muslim women that are 
    permissible for you to marry that which will leave you with no need for 
    that, and will keep you chaste and protect you from haraam. 

    And Allah is the one who blesses and honours those whom He 
    loves and is pleased with. 

    And Allah knows best. 

    See also the answer to question number
    103543.