I haven't read the other answers yet 'cuz I don't want to be influenced, so apologies if I'm repeating some obvious stuff.
>> What do you think it would actually be like to be a SEAL?
The first thing that came to mind was "long stretches of boredom punctuated by terror" but I think that was more apt for young soldiers in WWII than it is for SEALs. Maybe more like long stretches of training and waiting for the go-ahead, interspersed with brief stretches of intensely focused and highly satisfying activity.
My guess is that fear is a part of your life when you're on a mission, but it's fear that has been tamed and integrated. You acknowledge its messages giving you needed information about your environment (6th sense or whatever) and then you set it aside and get to work. (On a side note, some of my Buddhist training was about learning to deal with fear in this way--which is not to say that I learned those lessons!)
The parts of a SEAL's life that I think I would enjoy or would like to have more of in my life are the sense of purpose (the missions), the challenges to exceed your limitations, and the teamwork. I've mentioned before how much I enjoyed working with a top-notch team (in my case, engineers in a high-tech startup). In the teams you form bonds with people you can and do trust with your life -- those are precious and not something most of us experience, at least not at that intensity level.
What I think would be tough would be separation from home and family, physical exhaustion (yes you can handle it but eventually it wears you down), and frustration with some of the politics and chain of command. I don't pretend to know your political leanings or those of your teammates but I imagine that the military-political bureacracy is an equal-opportunity frustration machine.
>> What do think it would be like to be married to a SEAL?
For me, really hard because he'd be gone so much. I'm not sure how much I would worry about his safety, but I know I'd be lonely. I don't think faithfulness would be an issue. I would never marry someone I didn't fully trust, and I have never had an interest in someone other than my mate. (Viggo doesn't count!)
I ask myself whether I would marry a SEAL or anyone who would be away that much and my first thought is "no, rather not" but then reality is that you can't always choose whom you fall in love with. And if the guy was the one for me, then we'd figure out a way to make it work.