This guy has told my friend that he wants to marry her, have more kids, etc. He asked her to transfer to a grad program near him so they don’t have to be long distance. So if he’s trying to hide a wife, he’s doing some really silly things to tempt fate. She’s not going to drop her grad program and relocate, she says, so I’m not worried about that particular catastrophe happening, though it would be bad if she accidentally got pregnant while in grad school.
She hasn’t e-mailed me back either. 
I agree and I watched it happen to a woman I worked with, although I didn’t know her well. Even so, there are a lot of similarities in the two cases and that’s not to say it’s the same guy.
I was also thinking that this sounds exactly like a pathological liar.
I’ve known at least two such in my life, and the key to understanding them is to understand that they don’t always make up lies just to benefit themselves, like a normal (but scummy) person would; they lie all the time to construct a more exciting world for themselves - one in which they are important (rather than some impotent wage-slave, some sort of secret agent or in this case military dude on special ops).
One reason that they sometimes get away with it is that the lies are so outrageous and pointless that (some) ordinary people can’t even believe someone would tell such a lie basically for no reason. And often they have nothing obvious to gain from the lie.
Example: many years ago my wife befriended a woman who worked at a business she also worked in. She (the woman my wife met) was in a fairly humble part-time clerical position, and was single, overweight, rather plain and quite a bit older than my wife; but she was a pleasant seeming person, they got along well, and my wife didn’t yet know many at this organization. So they started to do lunch together.
Well, one day my wife tells me that, after dropping many hints, this woman told her a big secret - that in fact her job was a cover. In reality, she was working for the RCMP, the Royal Canadian Mounted Police. The reason for working this job was to keep an eye on some sort of big drug transactions being laundered through their workplace.
I suspected right away that this was total bullshit, and told my wife so. At first, she was reluctant to believe me. Why would her new friend make up such lies? She had nothing to gain from it. I pointed out that real undercover RCMP officers probably wouldn’t tell the first person they go out to for lunch all about it.
As time passed, it became more and more obvious this woman was a pathological liar. Her alleged duties involved seducing various gang members into revealing their secrets, something that even my wife recognized was pretty obviously wish-fulfillment fantasy (this woman was not femme fatal materiel). They also involved staying away from work for longer and longer periods for increasingly absurd reasons, which inevitably got her fired.
The point is that my wife, who is a very intelligent woman, more so than me in some ways, was taken in - at least at first. The reason, I think, is that she is so honest herself, she simply found it hard to believe that someone would lie so outrageously for no particular gain.
The liars I’ve run into (I’ve known at least three in my life) lie even when they don’t have to. It’s part of normal conversation to embellish a story for them, when the truth will do just as well.
Let me preface this by saying that the guy is almost certainly lying. However, what he says is not ‘impossible’. If I was the liar, and you grilled me for details, I could say something like this:
"I was an engineer in the coast guard, working on diesel generators. After I retired, I didn’t want to do manual labor any more, so I went to work at the library. Well, it turns out that a lot of decommissioned diesel generators have found new life as power sources for remote villages around the world. There’s a few of them in Afghanistan. The Green Berets have been working with the indiginous population on various ‘hearts and minds’ programs, including installing some diesel generators. They’ve been having problems with them, and there’s a shortage of people who really understand them.
So, I got a call and an offer to go over for week or two here and there and share my knowledge and help get things running. The offer was pretty generous, so I set up a construction consulting company, and on occasion I fly wherever I’m needed and help out. The money’s good."
Or something along those lines. I don’t know if such generators are actually in use, but I have a friend who was in the coast guard, and he does exactly that kind of consulting (not in Afghanistan, but general engineering-type consulting based on his knowledge of specific types of engineering used on coast guard ships).
That said… He’s almost certainly lying. While you could come up with a story that’s remotely plausible like the one above, it’s highly unlikely. My guess: Vacation with the wife and kids.
Is your friend smart enough to look at his wedding ring finger to see if there’s a tan line or indentation where a ring would go?
Well if he served more/ate less of it, he wouldn’t have become so fat/puffy/out-of-shape. I’m just glad the bad guys never figured out the extent of his martial arts skills were Father-Son-Holyghost, Father-Son-Holyghost, twist the guy in front of him’s wrist. 
All this is missing is, “Yeah, that’s the ticket!” 
Is his name Bond, James Bond?
If not he’s full of poo, married with kids and more likely than not he has other girls in other towns
Yeah, there was this one chick I know of, and when she was in her twenties she met this dude in his forties, and he was all like “I’m the Prince of Wales. My mother is the Queen.” Needless to say, it ended unpleasantly. 
Anyway, in seriousness I knew a girl who started seeing an ex-SAS guy who was a loudmouth about his current secret ops. For various reasons I won’t go into, we discovered that pretty much everything he said about himself was true - but he was lying to her about other stuff, including cheating on her.
In conclusion I suspect anyone who is some kind of spy and brags about it is a dick too; probably just as much of a dick as someone who isn’t and makes shit up.
So he makes the trip to see her, but your friend has never been to his place? If tomorrow, after an over-excited bit of lovemaking, he had a heart attack and dies in her arms, would she be able to tell a police inquiry his real address , his landline phone number, or ANY verifiable details?
( Oh, saying that “he loves me” doesn’t count))
Even if he had never told her the stuff about being a spy, by this point in their relationship he should have let her get acquainted with much more about his life. By this point, he should have:
Anyone who doesn’t do that eventually is probably lying about something, even if it isn’t about something as obvious as being a spy.
Could be that he only makes offers he knows she won’t accept. It looks like a yearning for permanence, but he won’t have to put his money where his mouth is.
Huh. I call mine “Little Ben.”
If my friend actually had a dialogue with me about this whole thing, I’d bring up the things on Wendell’s list. But she hasn’t written me back, which does not bode well. She’s probably pissed off at me. So it’s out of my hands until she responds, if she does.
What exactly did you say to her?
I’m not going to post my personal e-mail on here. In sum, I told her I thought about what she said about her BF, and that I’d asked around and it sounded unlikely to me that he was really special ops, and why. I told her she should ask some questions about that 11 day absence. That I was just worried about her and was concerned, and that if she wanted me to STFU and mind my own business, I would do so immediately.
Isn’t one of the whole points about being a spy that you don’t brag about it?
I think you were being her friend. You expressed concerns about his lies, said you were worried about her, and asked that she follow up. If she doesn’t want to hear it, well, unfortunately, some people have to pee on the electric fence themselves.
Give her time to think about it. All you can do is warn her, which you’ve done. After that, as long as she’s a legal adult and legally sane, the rest you can do is be there to pick up the pieces.
I know we all wish we could stop people from hurting themselves, but sadly, a lot of wisdom comes from the pain.
…and that’s gotta hurt worse for a girl.
That’s what I mean: if you are genuinely a spy, and you also brag about it, then you’re obviously a really bad spy, like the asshole I mentioned above.