The default commission you receive is as an Ensign in the U.S. Navy Reserve. Your billet is Strategic Sealift Officer. However, midshipman may apply to other reserve/guard branches as well as Active Duty. In other words, every branch (active and reserve/National Guard/Air National Guard components) are open to you. The NOAA Corps is also an option, but not too many people go that route.
Your
designator is Strategic Sealift Officer, 1665. Not every branch is open, i.e. there isn't a way to directly commission into the reserve component of the Coast Guard and I can't find the last graduate to go straight to BOTC for NOAA (...you can read the BOTC Bios for yourself here..
http://www.noaacorps.noaa.gov/botc/classrosters91topresent.html). You can go ANG, but that gets tricky, because you'll go spend 3 years learning to fly and then have to figure out how to fulfill your last 2 years of sailing commitment to MARAD because you won't be on active duty anymore. It is nice to say you can go into any branch, but it really isn't that simple, case by case can be difficult. The SSO program is designed for people to be able to fulfill the sailing commitment and the reserve commitment, so it is by far the simplest option. Other things are possible but they can get tricky in a hurry.
Your commitment is 8 years in a Reserve/Guard component
Generally this is true, but it is worth noting
46 U.S. Code § 51306:
(4) apply for, and accept if tendered, an appointment as a commissioned officer in the Navy Reserve (including the Merchant Marine Reserve, Navy Reserve), the Coast Guard Reserve, or any other reserve unit of an armed force of the United States, and, if tendered the appointment, to serve for at least
6 years after graduation from the Academy;
However the SSO Program requires an 8 year commitment, so for most it will be an 8 year commitment. However, if you could talk another branch into a doing a six year gig (...army reserve maybe?), you would still be compliant as far as MARAD is concerned.
On your marriage question: No, you cannot marry while you are a midshipman. You may certainly get engaged, but marriage is grounds for separation. There are a few midshipman that get married right after graduation though.
You can be married. One of my classmates got hitched over Christmas break. I direct you to the midshipman regulations:
"217. Marriage:
Midshipmen may be married. However, married Midshipmen will receive no special advantage in the form of leave, medical coverage, housing or privileges. The Academy assumes no responsibility of any kind for the dependents of Midshipmen."
