1. There's a lot of hassle with the name change. First you have to decide if you want to take his name at all or just keep your name (which depending on the man this can be a fight waiting to happen), will you take his name alone or will you hyphenate. And if you do decide to change there's having to go to or call all the appropriate places and lines- DMV, Social Security, your employer, the carriers of bills in your name (it will probably be the only time your marriage certificate is seen so much) and in some cases you get to hear the reps from these places give their opinion about your decision (like you didn't get enough from the people in your life already).
2. If you already live together, the only difference is now you will have a ring, a title,different way of filing your taxes and a certificate put away somewhere, that's it.
3. Obviously marriage implies that you want to be together forever, now think about that word FOREVER, because before you actually marry this word sounds very romantic, very appealing but when you have your first big fight or disagreements that pile up or if you start to take stock of all the annoying habits that aren't going to change it will seem more like a sentence being handed down.
4. Things WILL change between you and your single friends, you are now the married friend, the friend that is not first on the list to call to party till dawn, the friend who all of a sudden they feel will not understand their single person problems (and this kind of goes both ways with your marriage problems), and do not gripe to these friends about money because it will always end with "At least you have (insert husband's name here), I'm on my own." You have automatically become the dependable friend, the friend who throws dinner parties as opposed to blow outs, the friend who might have money to borrow, the friend who from their perspective (and sometimes yours) is tied down. You are also the friend who might share with her husband any info that might be shared with you, so sometimes this curbs what is shared with you.
5. Whether you realize it or not when you were dating/ living together/ not married it was it in the back of your mind that if things don't work out you can just pick up and go whenever you want, when you're married this is still true of course, but it has a bigger price. First you would have to pay$$$ to leave, second instead of being able to say "we broke up" you'll have to say "we got a divorce". Third you are not single again, you are divorced.
6. This is kind of an extension of #5 divorce. The word divorce will have new meaning to you. It will imply many different things ie. final, I couldn't make my marriage work, I've broken my vows, I'm not married, I'm not single, I'm divorced to name a few. The idea of divorce will seem similar to the idea of the scarlet letter yours being "D" and all that it implies not only to you, but what you think it implies to others. For this reason this word and it's idea will actually sometimes be a blessing and a curse for the same reason- it will make you want to stick it out, the days of the simple (if it was ever simple, but more simple) parting of the ways is over.
7. Any preconceived notions you had about what your life together forever would be like were daydreams. Don't get me wrong you can have a happy life together, you can have all the things you planned to have together, but there IS work involved. Marriage does not solve problems, it can actually give you new ones, it does not change the core of who people are, it is not a fix for anything that may be broken in the relationship you already have, and you both will have to work at it together to make it work, just like before if not more so.
8. Listen to the vows, to love honor and cherish, for richer, poorer, in sickness and in health, for as long as we both shall live. They ring like that word forever, romantic, appealing, but they are in fact a premonition of what is to come. You will have hard times, and those hard times will put strain on your relationship no matter how hard you both try to rally together. You may think back to the day you made those vows and realize you didn't really know what it would mean when you made them until now. I'm telling you, you never know what life is going to throw at you, but you should know (if you don't already) before you make these vows that they will or at least could happen and be prepared.
9. Me time. These two words may have sounded funny to me before, but they are necessary in my vocabulary now. When you marry it all becomes "we". We, we, we, we. I'm telling you now and start it early on you still need there to be "me". In the beginning we sounds great, the thought of it is great, but you will not want to do everything together, you will not want to talk about everything together, and you will not want everything, all the time to be we.
10. Privacy. Privacy as you know it is gone, even as I've been typing this my husband has come to glance at what I'm doing at least three times. Unless you go in the bathroom and LOCK THE DOOR privacy does not exist.
I'm sure I may have more to add as time goes on, but so far these are the things I have noticed that I didn't know about being married before I got married. Read at your own risk and share any you think I may have missed or what you may have learned yourself.