It's funny how people think getting married automatically takes you from "great relationship" to "disaster". If you have a great relationship, there's no need to fear marriage, especially after 5 years.
But, every long-term relationship, marriage or not, will eventually see it's problems. Whether you get married or not, you will encounter them.
What should you prepare yourself for? Well if you don't live with him, the main difference between where you are at now and where you will be after marriage would be having to share your dwelling space with another person. For some this can be difficult, for others not so much. My husband and I lived together before marriage (the
responsible thing to do, IMO) and so when we got married, nothing really changed at all.
In fact, that really sums up the difference between our relationship before we got married, and our relationship after we got married: Nothing really changed at all. We're still the same people having the same great relationship, we're just.. husband and wife now, instead of boyfriend and girlfriend. I guess one change is that we file our taxes as "married" instead of "single", hardly a huge change
But for other people, just the actual act of getting married seems to throw them into relationship turmoil.. I'm not sure why. Most of the time, I think it's because the two people weren't prepared. Often this comes from not having taken the steps to understand what sharing your life, in the same house, with another person will entail. It comes from not understanding how to communicate, how to compromise, and how to just live with each other for long periods of time (aka forever). It comes from two independent brains having to share a co-operative space, and then fighting against each other for supreme control. You can't
do that in a marriage, but.. you also can't do that in a long-term relationship either really.
A five-year relationship isn't very dissimilar to a marriage. Five years is a long time.. by now I assume you know you fit well together, you communicate, you compromise, you problem-solve.. if all these things are true, you are probably set up very well for a great marriage. So stop procrastinating and get it done already
You want the "pros and cons" of marriage. Well I can't really give you those, because it differs for each individual. For me, the biggest pro I can possibly think of is that my husband loved and respected me enough to make a commitment to the public that he was going to stay with me for the rest of his days, to the point where he'd risk losing half his stuff in the process if it didn't work out

For me, the pro is that I have an amazing and loving partner to spend the rest of my days with, and he wasn't so scared or lazy as to just say "You know what, forget marriage, let's just live together for the rest of our lives."
If you want the biggest "con" of marriage? I guess I'd say it would be divorce. And I
am divorced, and re-married, so I know how big a con it can truly be when the relationship goes down hill. Divorce is complicated.. but, I married a guy I barely knew, so what did I expect? I didn't have a solid relationship with my first husband, and we just weren't compatible. We knew nothing of what it took to make a marriage work.. we weren't ready, we were stupid and naive, and I'm pretty sure neither one of us understood what love itself even was, nor were we in it (love, that is).
At any rate, you are asking us to describe the pros and cons of a life-long relationship.. but you are already well on the way toward one with your five-year start. Courting Couples who have mostly been together a matter of months if not only 2 maybe 3 years max, got
nothing on you guys! What can they tell you that you wouldn't already know? What can I tell you that you wouldn't already know for that matter, as I've only been with my husband 2.5 years (6 months dating, 6 months engaged, 1.5 years married) which is only
half of the time you've spent with your existing boyfriend.
I'd say you should be giving advice to us on a good relationship, not the other way around.
At the end of the day, that's what it boils down to: If you have that good relationship, you are not going to see some hugely negative change from dating to marriage. You are going to be able to enjoy having a loving marriage that should last the rest of your days.
To me, that really is the only pro I could ever hope for. *shrugs*
It's not us that needs to tell
you what marriage is good for
in your life. You've gotta tell
yourself what marriage means for you, and why it's important. Don't let the rest of us define your life.