He has repented from a haraam relationship; should he marry his former girlfriend if she becomes Muslim?
Question

                I have been a muslim all my life and I have done some terrible things in my that has cause some great distress in my life. I have been with a Christian girl for 2 years now but recently seperated from her because I have came closer to islam. She understands that we should not be together right now. I know that I wasn't a good muslim before but now I want to do anything to be for given for what I did. We have done some sexual things like fondling, manual pleasure, and oral sex on one occasion. I know that these are grievous things and I beg Allah for forgiveness and regret what I have done.  This was a result in my ignorance and I have repented. I now pray 5 times a day, go to the mosc, and read Quran. I never want to go back to the bad things that I have done. I feel that I should marry a muslima from Egypt and change my life but I also feel that I should at least show the Christian girl islam in hopes that she will convert.  My questions are: Should I marry her if she converts? Or should I find a muslima and start a new life? Will I be forgiven for what I have done?.
Praise be to Allah.
    Firstly: 

    Feelings of sin and regret for what one has done are signs of 
    divine care for the one who committed the sin and serve to motivate him to 
    follow the right path after having gone astray. We do not want to give the 
    impression that what you have done is something insignificant, rather you 
    should realize that what you have done angers your Lord and that it is a 
    major sin. But we want to show you the path of repentance and let you know 
    that even though Allaah is not harmed by your sin and has no need of your 
    repentance, still He has helped you to repent and He rejoices at your 
    repentance. 

    You have to give up your previous sin, and sincerely regret 
    what you have done, and resolve firmly never to go back to this sin. 

    You should never despair of the mercy of Allaah, for Allaah 
    forgives all sins. All you have to do is to repent sincerely and after that 
    you will see that which will bring you joy; and seek the pleasure of Allaah.

    See also: 624,
    13990,
    34905 and
    22912 

    Secondly: 

    You also have to end your relationship with this woman lest 
    you go back to sinning. The basic principle for the repentant Muslim is that 
    he should keep away from all environments in which he used to disobey Allaah 
    and he must avoid and shun all the means that could lead him to fall into 
    sin. 

    So we do not think that you should get back in touch with 
    this woman, even with the intention of calling her to Islam. You have to 
    save yourself first. Who can guarantee that if you go back to sin – Allaah 
    forbid – you will be enabled to repent again? 

    You could ask some trustworthy Muslim women to contact her 
    and call her to Islam. We do not think that you should be the one to do 
    that. 

    Thirdly: 

    We do not think that it is permissible for you to marry her 
    as she is at present, not because she is a Christian, but because she is not 
    chaste – according to what you say. Allaah has permitted us to marry women 
    from the people of the Book, but that is subject to the condition that they 
    be chaste, i.e., they do not commit zina or have boyfriends. 

    See 22303 and
    2527. 

    What we advise you to do is to marry a religiously-committed 
    Muslim woman who will help to protect your religious commitment and help you 
    to do good and to obey Allaah. This is the way to success. 

    See 20227 and
    8391. 

    And Allaah knows best.