Salam seeker,
You can raise children and have coitus outside the constitution of marriage but it is sinful and is an act of unbelieve.
Here are two Ayats where you can read that marriage is concept made by the creator.
Sura 16:72
"And Allah has made for you mates (and companions) of your own nature. And made for you out of them, sons and daughters and grandchildren, and provided for you sustenance of the best: will they then believe in vain things, and be ungrateful for Allah's favours?― (72)"
It is also orded for the elders to encourage the young one to marry if they are able to it.
Sura 24:32
"Marry those among you who are single, or the virtuous ones among your slaves, male or female: if they are in poverty, Allah will give them means out of His grace: for Allah encompasseth all, and He knoweth all things. (32)"
You also find some of articles of Joseph who will answer your question.
regards