Eirinn - I've been a Naval wife for 25 years and a Forces brat before that. You can't make plans that are set in tablets of stone I'm afraid - you have to go with the flow and learn to be flexible.
For example, dh rang me one night - I said it sounded noisy and was there a Mess dinner (he was supposed to be in the Wardroom), and he said he was at Heathrow, off to Italy, would ring when he could, and didn't know when he'd be back in UK. He was given 2 hours notice of going. It meant rearranging my life for several weeks and going to things his family had planned 3.5 hours away with a small, but that's life.
Another time, he was sent to sea at very short notice one Christmas Eve, leaving me with a brand new range I didn't know how to work, plus his parents and grandma for Christmas. He wasn't back until well after the New Year, and no-one knew when they'd be back. He missed ds's birth as well as he was at sea; his grandma's 90th birthday celebrations (on duty elsewhere). You have to be adaptable and recognise that the job always, always comes first.
You will not be able to live on a base with him in Army accommodation unless you are married; you would have to rent privately.
The separation can be tough, one Lt-Cols wife I knew had done 8 moves in 12 years. You need to look further down the thread for advice from the Army wives; some will move around with their dh's every posting, some will choose to buy their own home and weekend, but weekending for long periods of time is tough - the longest we've done it for at one stretch was 4 years, and that was enough.
It can be tough, it can be lonely, but it's fun, and dh has had a great career. There's a good social life if you want it, and the opportunity to make lots of friends.