We should know that Allah has not prescribed for a Muslim woman to arrange her own marriage; rather He has stipulated that her wali (guardian) should be the one who arranges her marriage. He has prescribed that out of His mercy so as protect the woman’s interests. You must have heard the stories of marriages based on that (love marriages) and how their lives turned into distress and regret, if the marriage even survived.
What we advise the questioner is not to insist on what you think is right. Do not let emotions sway you when making decisions. Do not look at your problem alone; rather seek the help of a sincere and trustworthy family member or relative, who knows you and him, and who is liked by your father and whose opinion your father trusts.
Then pray istikharah to Allah and remember, when you ask your Lord for guidance by praying istikharah, turning sincerely to Him and expressing your need for His help and guidance, that Allah decrees nothing but good for His slave, whether His decree is in accordance with what you like and want or not. For the believer’s affair is all good. So be content with whatever Allah decrees for you.
You can also seek the help of someone who can convince your father to let you marry the one you want, if he has religious commitment and good character.
Do not try to start an argument with your father which may lead to him forbidding you and being harsh. Rather you should only deal with him in a gentle manner, and give him the impression that you accept his decision, such as saying, “You are my father and my guardian, and you know what is in my best interests, so I hope that you will think again,” and other such words that leave room for discussion. Do not seek a hasty answer from your father. The longer it takes, the more likely there will be a solution, in sha Allah.
But before and after all that, you need to turn to Allah making du`aa’. I do not mean only saying du`aa’, I mean turning to Him and beseeching Him, asking Him for goodness, relief and help. When Allah sees that you are sincere in your du`aa’, He will give you want you want, by His leave. How can it be otherwise when He is the Most Kind, Most Generous?
Although you feel so critical of your father and regard him as the one who is preventing you from marrying this man, we would not like you to forget that the relationship between a man and a non-mahram woman can only reach this degree of emotional attachment if there has been a great deal of neglect concerning the sacred limits set by Allah with regard to the relation between the two sexes.
You have to fear Allah, and beware of losing your religious commitment, which is the true calamity. A husband may come and go, wealth may be acquired and lost, but all that is insignificant in comparison to losing your religious commitment.
If you have done anything that is considered a transgression to Allah’s limit in this regard, then hasten to repent from it. Allah may be withholding your father’s acceptance until He sees that you are both sincere in adhering to His Commands. Allah says in His Book, “And whosoever fears Allah He will make a way for him to get out (from every difficulty).And He will provide him from (sources) he never could imagine. And whosoever puts his trust in Allah, then He will suffice him. Verily, Allah will accomplish his purpose. Indeed Allah has set a measure for all things” [At-Talaq 65:2-3]