As you should know in Islam, we are not allowed to keep an illicit relationship. There is no concept of boyfriend and girlfriend in Islam.

 

So, if you have been guilty of such a sin, I would advise you to seek repentance.

 

Once both of you have done so, you may marry; it is good for you to get the blessings of your parents; if they are just refusing based on materialistic considerations, you are allowed to go ahead and marry her.

 

If you do so, you still need to continue to keep good relations with your parents and honor and serve them as best as you can.