The old "marry your best friend" line, may have become a cliche, but that doesn't mean it's wrong. If you can talk and laugh together, and just hang out like buddies, your life together will be better and easier for it. But that's more or less been said by the previous posters. My addition to the conversation is this:
Be apart from each other.
By that I mean a lot of things. Travel separately once in a while. Have your own private spaces in the home. Go out with friends separately. Have a couple of not-mutual friends, even. Pursue your own hobbies and interests.
A little room to be yourself and be all by yourself is good for you as an individual and good for the relationship. You give each other time to be just yourselves (not just half of a pair) and come back to each other with new things to talk about. Win-win!
