Is marriage compulsory? I don't not think so. I am yet to see any law which says it's citizens must marry. Even the holy book never made marriage compulsory but only admonished.

It is undeniable that there are so many benefits of being married but still that doesn't make it compulsory. It is more it is expedient but not a law. If you marry, well, two good heads are better than one then there is procreation and legal satisfaction of sexual urges.

It is important to marry and procreate so the human race can continue but it is not binding on anyone. If it is a law in some countries, I would love to read about it.