Praise be to Allah.
It is true what you have said, that wrong is wrong. In Islam, pre-marriage relationships are not permissible. We believe that adultery is not permissible not only in Islam, but also in all religions of Allah (God). I believe that the gentleman of nationality Xyz whom you are seeing is not serious in getting married, because if he were, he would have married you from the very beginning. In Islam, a man must respect the will of his parents, and in some cases he must obey them. You, in your present status, are not a member of his family. When you become his wife, then you are considered to be his family. Yet even then, if a father orders his son to divorce his wife because, for example, she has bad reputation or she is not a good Muslim, he must obey his father. My advice to you is to think seriously in embracing Islam, not for the sake of this man, but for the salvation of your soul and body from Hellfire. I believe by now, you have a good idea what Islam is, putting aside the bad example this gentleman has been setting. Therefor, you should stop seeing this man and you should become Muslim. If his love to you is genuine, he will propose to you. If he doesnt, then be sure that Allah will not leave you alone, and as He guided you to his religion, He will send you a good Muslim who will cherish you and give you a decent life as a wife not as a mistress. I pray to Allah that He may enlighten your heart with Islam and guide you to make the right choice.