Pretty much in same position here, maybe a bit beyond. At first my wife used to get mad when I opened the subject of her being with another. Now we can discuss the possibilities. At first she also felt she'd be betraying me, used to say I'm enough for her, now we are also over that but she still has moral inhibitions, probably because of her upbringing and our community here. I'm not in the military but also away from home for work for long periods and she knows she could proceed with this without me.
cuckoldbydave's suggestion is reasonable. I have always approached her in the "this is for your pleasure" route and have not progressed in reality. The logic if it's "for her pleasure" she must first admit that she is not getting enough pleasure from you which is not in a woman's dna to do if she wants to stay is very acceptable. Maybe from now on I should emphasize that it would be my pleasure watching or knowing she was fucking another man.
And what a nice coincidence, when I'm away from home I also periodically keep sending her tumblr pics with Hotwife captions and she is also intrigued. I was hoping to discuss about them when I was home last week but never found the right time because of the kids and my back pain condition