Please don't take any of what I am about to say as putting you down. We were all 19 once with big plans for a perfect future. Unfortunately reality doesn't mesh with those visions. Things become more difficult than we imagined they would be, and the excitement wears away with time.
But, it's not all bad news. In fact, once you are prepared for things, they can't disappoint you. So, let me help you a little with some advice that you can take or not.
First, the schooling will be the easy part. He'll be putting in long hours but he will be home for some part of every day. After school is over, he will be away for weeks or months at a time. There will be times when you will have gone so long without hearing his voice that you will forget what it sounds like. He will be nowhere to be found when your car breaks down, or you make a subtraction error on your checkbook that leaves you overdrawn. He won't be home for Christmas every year, or your birthday, or your anniversary... etc. You may have to give birth to a child without him there to support you. You may suffer the loss of a loved-one while you are thousands of miles from your nearest relative - and he won't be home to see you through it.
On the other hand, he will be there for some of those things. He will not be gone all of the time - even if you begin to feel that he is. And you will recognize his voice the first time you hear it.
You may find the perfect job, your dream house, a neighbor who becomes your closest friend, and then get transferred away from all of that after a couple of years. Then, you may find all of those things again at the next duty station - or not. Be ready for this. It's a part of Navy life. It won't hurt nearly as bad as long as you have this in mind from the beginning.
Don't even utter the words "re=enlist", "retire", or "career" until he has been at sea duty for at least two years. No matter how much money they hold under his nose to reenlist, it may not be worth the misery. If the time comes that you BOTH decide to reenlist, then it will be a decision that you will have made with full knowledge of the consequences. Right now, his future career intentions mean ZERO because he doesn't really know yet what it is really like. So, don't wipe the idea of reenlistment or retirement completely from mind just yet. But, by the same token, don't set your minds on them either. Be flexible and see what comes.
Because you are still so young, there will be plenty of time to work on things like saving for a house and raising children. Don't rush into anything. Also, don't rush into the assumption that Navy life will be miserable the first time it gets difficult. It will be what you make of it, and you can always opt to get out after one enlistment if it doesn't suit you as a family.
It's a tougher life than being married to a civilian, but the rewards can be great. You can make it quite well if you are prepared and if you use the resources at hand. There will be a network of spouses and others who can help you when he is away. Do not be afraid, or too proud, to rely on others when you need them. Also, make yourself as available to them as you can be. This will strengthen your ties to them.
Recognize that the wives of the officers and senior enlisted men will have bigger, nicer homes than yours. That is just a matter of them having been married longer and making better salaries than you. They will understand when you invite them over for coffee and your place is small and a little spare on furnishings. These things come with time and these people know this from having been in your position before. The important thing is that you form relationships with them anyway. You will all be very important to each other.
I tell you this because you say that you are not close to your family, and even if you were the geographical distance from them will mean that you need some dependable people nearby.
A lot of military marriages end in divorce, but probably no more than civilian ones. The difference is that people who divorce on active duty have the military to blame. But, the real truth is that most failed marriages fail because of unrealistic expectations. When they get to the "for better or for worse" part, you have to mean it. It's never going to be like the movies.
I can't tell you what is going to be the hardest part, or how to avoid or overcome it. That is different for everyone. The best advice I could give you is to see marriage - in or out of the Navy - and everything else as a thing that evolves over time. Let it grow and grow with it. Just as college life turned out to be very different from the way you imagined it a few years ago, marriage will not be what you think it is going to be like. So too will Navy life. That doesn't mean it will be worse - just different. Don't be disappointed if things are not the way you pictured them - almost nothing ever is. Take it as the challenge that it is. Enjoy it.
Good Luck and Godspeed to you both. Thank him for me for serving this wonderful country.