I'm not too far removed from that, at least it doesn't feel that way, so I'll take a shot.
At the Coast Guard Academy, dating between cadets was called "Darksiding".
In the class behind mine two cadets arrived at reporting in day as a couple. They lived in the same town and dated in high school. I believe the relationship lasted one or two years and they broke it off. I don't think it was because of the school though, maybe they just drifted apart.
Of the just over 200 of my classmates that graduated, probably around five ended up marrying each other. That's not terrible odds. MANY MANY more of us turned to the Dark Side at some point in our cadet careers. I visited the Dark Side three times myself.
Obviously it worked out for the people who married.
I have a few cautions.
1. Make sure you can control yourself. It's a military setting. If you can't keep your hands off of each other it might be bad news. You can't kiss, can't hold hands, can't be in rooms with the doors closed. When people do do this stuff, they will sometimes be caught and the iron fist will fall. You'll have to be inventive. As a sophmore I worked out a deal with the Wardroom staff to give me a table cloth, a few nice clear plastic plates, forks, knives, and cups. I got good juice at the exchange, and ordered out Chinese. It was a surprise for her, and it was a little Chinese dinner date. Not entirely professional, but at some point you'll have to live a little. Sexual misconduct in the barracks is a big Class I offense, and it is losely defined, so better safe than sorry.
2. Have some time apart. Academies have a way of putting the jets on a relationship. You have so little personnal time that when it is available you spend it with the significant other. That is a lot of "me" time with someone else, and it can burn you out.
3. Be prepared for rumors. The Academy Rumor Mill is unbelievably efficient. In no time your business, with your significant other will be everyone else's business.
4. If and when you break up, there is LITTLE room to get away. You will have to deal with the fact that you will see your ex dating all kinds of people. It will be in your face, you will not like it, and it will get old. I dated a girl that had a room in my wing area. Once we broke up, we still had to walk by each others rooms...not ideal. If you need room after a break up, an academy is a hard place to find it.
5. Be prepared to see them in the fleet or whatever service you will be in. The Coast Guard's small so the chances of a Coastie interacting with an ex is pretty high. It might be a little strange on the outside, or after some time if won't even matter. It all depends on how you handle it.
Now you're already dating your significant other, so a lot of this doesn't directly apply, but some of it does. Proceed with caution, but it can DEFINATELY work, I have many classmates with the same last names that can attest to that.
Good luck, I hope this was more helpful than a creepy stream of advice from a former Dark Sider.
I can vouch for the fact that dating classmates' sisters is not a bad idea.