I truly believe a majority of men would be happier, overall, not getting married OR living with a girl. I understand few women will tolerate "only" dating a guy, but this is how I see it, regardless.
Men might be assholes, but women are insane (some only slightly, and some in an alarming way). No matter how much she pleads her great love for you, somewhere down the line your relationship with her will be your potential undoing.
I hate feeling this way. Truth is, I am a romantic. LOVE the idea of "being in love". However, experience and wisdom points to a different reality than what is presented by tradition/societal expectation.
Without question, DO NOT even contemplate marriage before hitting, say, 35, minimum. MINIMUM.
In my line of work, I see that there are a couple of things that are almost always responsible, directly or indirectly, with destroying a man's life, legally-speaking: a) drugs/booze; b) WOMEN.
Never completely trust any woman unless she's your mother (and a decent one, obviously) or your sister.
When you let down your guard with a woman in a romantic relationship, you're already heading towards disaster. (And allowing a woman to live with you is a surefire way to slowly extinguish romance and open yourself up to heartache and trouble the likes of which you've never thought possible.)