...when you have given their due Mahr (bridal money given by the husband to his wife at the time of marriage), desiring chastity (i.e. taking them in legal wedlock) not committing illegal sexual intercourse, nor taking them as girl-friends... (5:5)

Verily, those who like that (the crime of) illegal sexual intercourse should be propagated among those who believe, they will have a painful torment in this world and in the Hereafter. And Allâh knows and you know not. (24:19)

All the boys who are after girls, what are they going after? To do the illegal things which would destroy the girl's life, they can use the girl, and call her a girlfriend, up to the limits, as long as she pleases them, and they can enjoy her beauty.

And whoever involves, themselves in these types of activities  them because, they are not followers of Allah, they are the followers of Satan, and they fool all the girls, use them only for fun, just like buying a doll from the market; to play with and get rid off. 

Satan gives every girl so much assurance, that he "loves" me only, and he is my "friend", and they wait from all of his wrong promises, and hopes, so they lose there modesty, dignity, and they destroy the life of the girl. 

Lets examine how the relationship regarding the keeping of a boyfriend works, see how girls fool the boy, the same way the way the boy thinks he is smart, and is the playboy of society. 

Each girl gives assurance to the boy, to bring all of his earnings to her, and to take care of her. And that she will be his best help, and without her he can't go anywhere. To keep buying her gifts, and perfumes, luncheons, dinners, ect. But all of these stories go to all the boyfriends, and the same lady when she meets other girls, she would tell them how she was fooling to her boy friends. This misbalances the system of Allah, and it is a early training for the boy and girl to be misguided. 

After the first stage, when they plan to be married, the whole life stays in doubts, and misunderstandings, no confidence and not trust. For example, whenever the husband is late from his work, or from the market, or maybe is involved in accident, because the lady was involved in this before, she has experience with it. When she use to hide from her culture and family and meet other boyfriends, she always would think, that her husband is also involved with another girl, because he is coming late. And when the husband reaches home, she blasts, and asks him where he was, and tell him that she is not a fool. And would say things such as "Stop fooling me I am sick and tired of you, and i am living in this house like a jail, I am not your servant, you have made my life miserable."

And this is the end of the love, and starts towards divorce. Now who is losing us or Allah (SWT)? 

If we follow Allah from the beginning, we would chose the same type of girl, the way we are.

The same thing goes to the girl, that if she is late from her work for example, and is late to pick up her bus. Any small excuse will create doubts in the heart of the husband. And when he starts to doubt his wife, even if she is talking to his brother, he will think there is something going on, because his eyes and mind already experienced matters such as this one. 

This is the exact reason why Islam prohibits this, and Islam is a guideline from Allah to the human being, and he is our Creator and Provider. And is the all knower of our chemistry. Our bodies' chemistry is based on flesh and blood, whatever actions are committed in the past, without knowing the punishments, whoever asks repentance from Allah, and chooses a right practicing Muslim, then there is no problem in this life. However whoever knows this, and still has a boy or girl friend, then he or she will be in the punishment of Allah here, regardless if he lives single or married. And in there hereafter there is only hell, because this is a major sin, whoever committed with knowing the punishments, will never be forgiven. 

Guide us to the Straight Way

The Way of those on whom You have bestowed Your Grace ^[], not (the way) of those who earned Your Anger (such as the Jews), nor of those who went astray (such as the Christians)

Any action which is from the enemies of Allah (SWT) and his Prophet, whether we would call them as "modern", or backwards. It leads towards the hell fire. Because these people are misguided by Satan, and Satan teaches them to do things which are against the will of Allah and his prophet, how can anyone without marriage touch another boy or a girl? This is the actions of animals, and are not human actions.

These are the limits (set by) Allâh (or ordainments as regards laws of inheritance), and whosoever obeys Allâh and His Messenger (Muhammad SAW) will be admitted to Gardens under which rivers flow (in Paradise), to abide therein, and that will be the great success. (4:13)

If you avoid the great sins^[] which you are forbidden to do, We shall remit from you your (small) sins, and admit you to a Noble Entrance (i.e. Paradise). (4:31)

Those who avoid great sins (see the Qur'ân, Verses: 6:152,153) and Al-Fawâhish (illegal sexual intercourse, etc.) except the small faults, verily, your Lord is of vast forgiveness. He knows you well when He created you from the earth (Adam), and when you were fetuses in your mothers' wombs. So ascribe not purity to yourselves. He knows best him who fears Allâh and keep his duty to Him [i.e. those who are Al-Muttaqûn (pious - see V.2:2)] (53:32)