Men especially.
I know of many people who had perfectly great relationships that lasted for years, and the moment they got married, it all went downhill...and they were divorced within a few years.

If it ain't broke...

Khalid, clearly you need that piece of paper to justify a relationship, and that's great for you. But many other people are fine simply being with the person they've chosen as their companion. They are quite happy living together, raising a family with that person, buying a house, co-mingling their finances...everything short of signing a marriage contract. And if that works for them, then more power to them.

To each his own.

"If you're looking for sympathy, you'll find it between sh*t and syphilis in the dictionary."
- David Sedaris