Praise be to Allah.
Having a girlfriend is haraam; the prohibition is indicated by the Qur’an and Sunnah, and by the consensus of the scholars. This applies if the man and woman have not committed indecent actions. Allah, may He be glorified and exalted, says (interpretation of the meaning):
“Tell the believing men to lower their gaze and guard their private parts. That is purer for them. Indeed, Allah is Acquainted with what they do”
Allah gives a similar command to the believing women, as He says (interpretation of the meaning):
“And tell the believing women to lower their gaze”
And Allah has enjoined women to observe hijab in front of non-mahram men, as He says (interpretation of the meaning):
“O Prophet, tell your wives and your daughters and the women of the believers to bring down over themselves [part] of their outer garments. That is more suitable that they will be known and not be abused. And ever is Allah Forgiving and Merciful”
And He has forbidden them to display themselves (tabarruj), as He says (interpretation of the meaning):
“And abide in your houses and do not display yourselves as [was] the display of the former times of ignorance”
And He has forbidden them to speak softly to non-mahram men so as to avoid negative consequences, as He says (interpretation of the meaning):
“do not be soft in speech [to men], lest he in whose heart is disease should covet”
The Prophet (blessings and peace of Allah be upon him) forbade a man to be alone with a non-mahram woman. He (blessings and peace of Allah be upon him) said: “No man should be alone with a non-mahram woman unless a mahram (or hers) is present.” Narrated by al-Bukhaari (4832) and Muslim (2391).
And he (blessings and peace of Allah be upon him) said: “No man is alone with a woman but the Shaytaan is the third one present.” Narrated by at-Tirmidhi (1091); classed as saheeh by al-Albaani.
And he (blessings and peace of Allah be upon him) said: “For one of you to be struck in the head with an iron needle is better for him than to touch a woman who is not permissible for him.” Narrated by at-Tabaraani; classed as saheeh by al-Albaani in Saheeh al-Jaami‘ (5045).
All of these commands and prohibitions are aimed at protecting a person lest the Shaytaan lead him on gradually and cause him to fall into major indecency of which Allah says (interpretation of the meaning):
“And do not approach unlawful sexual intercourse. Indeed, it is ever an immorality and is evil as a way”
And He, may He be glorified and exalted, said concerning it in Soorat al-Furqaan (interpretation of the meaning):
“And those who do not invoke with Allah another deity or kill the soul which Allah has forbidden [to be killed], except by right, and do not commit unlawful sexual intercourse. And whoever should do that will meet a penalty.
Multiplied for him is the punishment on the Day of Resurrection, and he will abide therein humiliated –
Except for those who repent, believe and do righteous work. For them Allah will replace their evil deeds with good. And ever is Allah Forgiving and Merciful”
The wise person will not be unaware of what results from a man taking a woman as a girlfriend, namely violation of honour and falling into shameful deeds which result in the mixing of lineages, breakup of families, and spread of disease; the abuse of the woman by taking her as a temporary means of fulfilling desires; and large numbers of illegitimate children who will grow up resenting society and not feeling that they belong to it, so they will spread mischief in the land; and there are other evil consequences that affect individuals and society as a whole, as a result of people taking girlfriends and boyfriends.
And Allah knows best.