Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Most probably a guardian of a woman always heeds for the benefits of those women who are under his guardianship. Hence, his approval is a compulsory condition for the validity of marriage. Indeed this condition helps gain successful marital life since the guardian is more experienced and has a sight further than the girl.
We think that your guardian has some reservation on this marriage for some problems he perceives and that may prevent you to have a successful life. However, if you are certain that he is a religious man and a suitable match for you then try your best to convince your guardian, if he agrees then Praise be to Allah. If he does not accept then you have to abide by what your father orders and this will be better for you. Make Dua to Allah to grant you a good husband.
Finally we inform you that it is strictly forbidden for a woman to have any kind of relationship with a man alien to her. Therefore, you have to immediately cut off all relations with this man through the net, the phone or any other means.
Allah knows best.