When you get married or when you decide to take the decision to live together, both are committments to the other partner... everything is exactly the same, except there isn't a marriage certificate...

Other than a piece of paper and being married before a Justice of the Peace or a Minister/Imam/Rabbi or whatever your preferred 'holy' man is, its exactly the same...

I have lived with a man and I divorced a man - two different people, and both time, the decision to end the relationships were hard... if anything, the divorce was worse in the sense that because I was his wife, I got screwed over financially... if I had just lived with him, I wouldn't have had to take the responsibility...