Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
It is not permissible for a Muslim man to have a relation with any woman outside marriage. So, you should propose to that girl and if she rejects your proposal, you should cut off your relation with her.
Responding to your question, Dr. Muhammad Salama, PhD, Islamic Studies in English, Associate Professor at the Faculty of Islamic Sciences al-Madinah International University (Mediu), states,
Islam is the religion of modesty and chastity that aims to build a community of virtuous men and women with pure hearts. This is why Islam laid restrictions that organize the relation and communication between marriageable men and women; for, without these restrictions, Satan would have a great opportunity to sow and spread corruption in the society.
So, basically, a man may not speak with a marriageable woman unless for a need or necessity and this has to be in a proper way and words and not in privacy.
So, brother, if you are serious to marry this girl, make istikharah Prayer (a prayer where a Muslim asks Allah to choose for him/her) and propose for her in a formal Islamic way. If your proposal is declined, you have to cut off your relation with her as it is basically prohibited.
Brother, we make troubles for ourselves by contravening Allah’s teachings. We need to follow Allah’s directions and let Him choose for us because He knows and we do not know.
Sometimes we love things and people and they finally turn to be a cause of suffering for us.
Allah Almighty knows best.