If you cohabitate with someone for a period of time and have a child with that person, you are legally married. You have to get a divorce just like anyone else, pay alimony, child support...all that good stuff.
For me, I would only get married if I wanted a family. Other than that, there's no need for marriage.
Other than the facts @EleGirl
posted re: Common Law Marriage, it's about more than simply living together and having a child or children together. To qualify the couple must also use the same surname, present themselves personally and professionally as Mr and Mrs, file taxes as married, share a residence, and must do all of the above for several years before having a Common Law marriage recognized.
In Canada, at least, it seems easy to fall into a Common law marriage. Here in the U.S., not so much. It's a very deliberate act that takes longer and is more of a bother than actually just getting married.
If marriage doesn't benefit women why do so many demand to be married but also initiate divorce disproportionately more than men?
Because, turns out, in most relationships the women handles the paperwork. I'm sure the numbers will change, though, because same sex marriage has become legal.
Personally, my exH and I were separated for over 2 years when I was finally able to file for divorce. By that time, I was living in a rental with my DH and kids while exH was living at his parents house with GF #28 (I exaggerate. She was probably #11. Too bad they didn't work. I liked that one.)
Why was I the one to file? Because he wouldn't. Apparently, it cost money and he didn't want to have to pay.
Accuse me to stirring up controversy if you want but there are financial incentives for women to divorce. That is a fact.
The reality is that there are incentives for the lower earning spouse to divorce. The law is gender neutral. Traditionally, it's been the woman who is the lower earner and so the idea of a bias was born.
There are also a lot of men who have contemplated/attempted/committed suicide because of marriage.
Absolutely not. No sane and mentally healthy person commits suicide with the exception of those who are terminally ill and suffering. Physically sound individuals who commit suicide do so because they are not mentally sound and not capable of sustaining their own lives.
In other words, the marriage, divorce, affair, whatever didn't cause the men you speak of to kill themselves. Mental illness did.