[dinosaur]

And, its not just about flaws and random idiosyncrasies...

-how do you divide household chores?
-who cooks? who cleans?
-what groceries do you buy? do you eat the same meals together?
-do you do your own laundry? does someone do it all and the other put away?
-financial issues: joint account for household expenses? who puts what in? is it a % of monthly income? is it an even amount? does one pay the rent\mortgage and the other pays for utilities? insurance? who is in charge of paying the bills?
-who pays when you eat out? what happens when one has money and the other doesn't?
-what time do you get up in the morning? what time do you go to bed?
-do you share a car? each have a car? who pays for gas when you are both driving together?
-What are your expectations of the other in regards to going out with friends? boys night? girls night?
-Whose family do you visit for holidays (Christmas, etc)?
-Socializing at your place (hosting parties), etc. Do you want to come home to a house full of females after a long day a work? Does she want to come home to a house full of dudes playing video games after a long day?
-what are you expectations about sex? 3 times a week? once a week? daily?
-are there kids in the future? does one parent stay home? daycare? family? how many kids?

The list goes on and on and although it may seem like stupid shit, this is the stuff that nags at you when you get frustrated. This is the shit that divides a couple after a while. This is the shit you need to know AND experience BEFORE you get married. Nobody likes to plan an exit or discuss these very un-romantic topics, but to have a successful relationship, you need to.

Like melloman said, how do you fight\argue\disagree when you can't just 'go home'?

An ideal situation would be you both living together and functioning well for at least a year before you sit down and SERIOUSLY consider committing your life together.