Praise be to Allaah.
This question requires that we offer advice to both of you. Firstly, to your father, who you say is preventing you from marrying this girl whom you describe as religious and well-mannered. He has to allow you to marry her, unless he has some legitimate Islamic reason, which he should explain to you to convince you and put your mind at rest. He should also put himself in your shoes: if his own father prevented him from marrying a religious and well-mannered girl whom he liked, would he not feel resentful about this denial of his freedom? If he would not like his father to do such a thing to him, how can he do this to his son? As the Prophet (peace and blessings of Allaah be upon him) said: “None of you truly believes until he likes for his brother what he likes for himself.”
It is not right for your father to prevent you from marrying this girl with no legitimate Islamic reason. If there is a reason, he should explain it to you so that you will understand what is going on.
Our advice to you is this: if you can possibly change your mind and find another girl to marry, in order to please your father, maintain family unity and avoid division, then do so.
But you may find that you cannot do that, because your heart is attached to this girl, and you cannot bear the thought of marrying anyone else. You may also be afraid that if you choose another girl, your father might object to that marriage too, because some parents may try to force their son to marry a relative, or a woman whose qualities the father likes but the son does not. Some parents may feel jealousy or envy even towards their own children, so they prevent them from doing what they want to do. If this is the case, then there is no sin on you if you marry her, even if your father objects. Perhaps after you are married, your father may change his mind. We ask Allaah to help you make the right choice.