Everything you don't absolutely adore about this magical human you've pledged yourself to is going to now manifest itself in wild screechy detail. You will fight about things you didn’t even register during those blissful days of moonlit walks and Sunday afternoon sex. Eventually, you will have to face a stunning reality: The person you are marrying is exactly who she/he is, and will never be anyone else. Not now, and not once you're married. Whether that's a beatific thing or a source of night terrors all depends on you. (Note that I didn't say it depends on your partner. If you don't like what you're marrying, then it's on you to either get over it or call it off. Sorry!!)
All your interactions will be weighed with a new gravity. When you do fight, it's fighting as a COUPLE THAT WILL BE MARRIED. Those things that were mere annoyances are now albatrosses draping your shoulders for eternity. (Seriously, it's no coincidence that Coleridge’s Mariner ranted to a wedding guest).
Melissa Lafsky lays down some harsh truths about what it means to commit to spend the rest of your life with a single person (and how weddings bring it all out):