It stands to reason that having a girlfriend/boyfriend is not the manner of a Muslim. It is forbidden for a male Muslim to have a girlfriend, as it is forbidden for a female Muslim to have a boyfriend.
Dr. Muzammil Siddiqi, former president of the Islamic Society of North America (ISNA) states: “Muslims should have good relations with all people, males as well as females, at school, at work, in your neighbourhood etc. You should be kind and courteous to everyone. However, it is not allowed in Islam to take a non-mahram person or persons of the opposite gender as a very close friend. Such friendship often leads to haram. In the Qur’an, Allah mentioned that good men and women are those who marry, do not have fornicating relationships and do not have “paramours” or Akhdan see An-Nisaa’: 25, Al-Ma’idah: 5).
Akhdan are “sweethearts” or for a man a “mistress” and for a woman a “lover”. The Prophet, peace and blessings be upom him, is reported to have stated that “whenever two strangers of the opposite gender are alone with each other, Satan becomes the third one between them.” (At-Tirmidhi)”
So, it is not allowed for a Muslim boy to have a girlfriend or for a Muslim girl to have a boyfriend. Howsoever pure your intentions may be, the danger is that it will lead you to sin. Or at least you will be alone with each other and spend more time together.”
Shedding more light on this, the eminent Muslim scholar, Sheikh Muhammad Al-Hanooti, member of the North American Fiqh Council, states: “A friendship with the opposite sex is not of Islam. It used to be of the Jahiliyyah (pre-Islamic era) style of life. A friendship of the two sexes can never be safe or sex-free. I agree that in some exceptional cases, it could be innocent. But, a law is usually amended for social regulations. There is no law to be customized for a certain person or few people.

The Qur’an and Sunnah guidance for the sexes dealing with each other has a main major issue for which Islam has set principles and rules to govern. It is the desire and lust. The Qur’an prohibits anything that motivates one’s heart in a seductive way towards the other. The Qur’an tells a woman when she speaks to a man to speak in a way that doesn’t show any interest in him lest he should feel seduced to build up an unhealthy relationship. If there is a possibility in any kind of action that it could lead by some percentage into catastrophe, no one will ever take that risk. I can say what you call friendship could have some percentage of leading into haram. How would you go to that risk whereas if a doctor says to you an operation of a certain organ could lead you into death? You would say I don’t want to risk my life, but I will take the pain.

Firstly, this is a deen but not a man’s opinion. Lastly, if you take it, you certainly will be on the safe side. If you want to follow reason, reason has a lot of defects and sometimes we cannot draw the line to know who is sane and who is insane. Sometimes you cannot know which is which.