If he is thinking of going SWO, yes, he will be gone a lot. Really, if he's joining the Navy, no mater what he does, chances are very good that he will be gone a lot. It's the nature of the beast.
What "a lot" means does vary from job to job, and even in the same job. He may be assigned to a ship that is out more than normal, or he may hit one that is going through a slightly lighter period. But he will be gone, and it will interfere with your life in a million annoying ways, and it will be frustrating. And even when he's home there will be times he stands duty and you don't see him much, or where he has to work weekends, or where he comes home from work and proceeds to spend the rest of the evening working. This is the inescapable reality of Navy life.
If this sounds intolerable to you, then no matter what he choses, it probably won't work out well for you.