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:
1- Indeed, your question should not be raised in that way as you, as a Muslim, especially in Ramadan, should never have such a relation with a member of the opposite sex.
2- Therefore, we advise you to cut off this relation immediately and repent to Allah Almighty asking Him for forgiveness and seizing the opportunity of Ramadan to draw yourself closer to Him via good deed and acts of worship.
In his response to your question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states,
I would urge you to repent and turn to Allah for forgiveness. Living with a woman without marriage, you should know, is the most heinous sin in Islam.
So, you should consider it a priority to break this addiction. You may marry her with her parents’ consent. That is the way to lead a lawful (halal) life. Then the above question would never arise.
Ramadan is all about shunning evils, breaking bad habits, developing good habits, and thus coming closer to Allah.
Hence, you should hasten to break up this relationship if marriage is not an option and seek repentance.
I pray to Allah to inspire you to seek repentance and help you remain steadfast.
Allah Almighty knows best.