In the name of Allah, We praise Him, seek His help and ask for His forgiveness. Whoever Allah guides none can misguide, and whoever He allows to fall astray, none can guide them aright. We bear witness that there is no one (no idol, no person, no grave, no prophet, no imam, no dai, nobody!) worthy of worship but Allah Alone, and we bear witness that Muhammad (saws) is His slave-servant and the seal of His Messengers.
Allah Says in the Holy Quran Chapter 5 Surah Maidah verse 5:
5 This day are (all) things good and pure made lawful unto you. The food of the People of the Book is lawful unto you and yours is lawful unto them. (Lawful unto you in marriage) are (not only) chaste women who are believers but chaste women among the People of the Book revealed before your time, when ye give them their due dowers and desire chastity not lewdness nor secret intrigues. If anyone rejects faith fruitless is his work and in the Hereafter he will be in the ranks of those who have lost (all spiritual good).
Al-Tirmidhi Hadith 3118 Narrated by Umar ibn al-Khattab
The Prophet (saws) said, “Whenever a man is alone with a (non-mehram)woman, the Shaytaan makes a third.”
The only legal relationship between a non-mehram man and woman is formed through the sacred institution of Nikaah in Islam; engagements, fiancé, etc. have absolutely no legal basis in Islam, and it is not permissible for a believer who sincerely believes in Allah and the Last Day to privately talk or meet casually with non-mehram women without any genuine and pressing need.
If one is engaged to marry, it would be best and purest to perform the ‘nikaah’ between them, for then they would become absolutely legal for each other. If for any reason whatsoever one is unable to perform the ‘nikaah’ at this time, the only way the two can meet or talk is if the girl is accompanied by a male mehram guardian member of her family (like her father, her uncle, her brother, etc.).
But to simply talk casual or vain talk to the person to whom one is engaged to without the presence of the mehram of the girl would be a clear violation and transgression of the Laws of Allah Subhanah and thus a sin in the Sight of the Lord.
Whatever written of Truth and benefit is only due to Allah’s Assistance and Guidance, and whatever of error is of me alone. Allah Alone Knows Best and He is the Only Source of Strength.
Your brother and well wisher in Islam,