her situation isn't that uncommon among military spouses. her feelings for both her husband and her good friend are real. i love my friends, and some of them i could see myself happily in a relationship with, if i wasn't already involved (and if they were single as well). however, i don't allow myself to think abou the possibility of being with any of them, because i love and am very much *in love* with my partner.

she committed to her husband and chose him over all of the other men she could have chosen...there had to be a reason for it. when she starts having thoughts about the other guy, encourage her to instead think about her husband and what it was about him that attracted her to him. if her feelings toward the friend don't fade back into "just friends", she will have to make the choice to either carry on an affair, or tell one of them that she's sorry, but he's not as good as the other guy in her eyes. that would be a very hard thing, too, and she has to consider whether she's going to be able to do it.
in the meantime, she's got a great friend in you, and i know you're torn about how to help her...just be there, let her talk it out and maybe help her find an interest in something that's just for the girls, so she won't dwell on the fact that her husband is away. sign up for an all-female yoga class, or set up a standing appointment to have manicures/pedicures, maybe even finding someone on base to babysit for the two of you and have a weekly "girls only" night. get a bottle of wine, your favorite "pampering" foods (death by chocolate cake, brownies with lots of icing, ice cream sundaes...you get the idea ) and a good chick flick. or a video of your favorite stand up comedian(s). create a perpetual calendar with note cards, with a special thought each day for the husband and for you two as well (ie, monday - think about what your favorite food to eat off your partner is, tuesday - what's your favorite body part to lick...to have licked?, wednesday - what's the first thing you noticed about your love?, etc..)that can be flipped back to the beginning and used each month to remind both partners of each other.
good luck to both of you. i know this has to be hard on you, too, as it reminds you daily that your love is away, also. chin up, girl, you're definately someone special