There is usually something wrong with the marriage before the deployment.
Lots of soldiers use deployments (by volunteering) as an excuse to escape instead of staying home and dealing with marriage/kids. Then they tell their spouses but the military is making me go! And there are plenty, numerous, affairs that go on between soldiers while deployed. I've seen that with my own eyes.
Not that it excuses this woman's behavior. But in my experience (and we've seen this a lot in our 24 years in the AF) there is almost always more to the story.
Sometimes the spouse says nothing, when the soldier comes home, there's no one at the airport to meet him, and when he gets to his house, its empty. Usually the leaving spouses uses the "I didn't want him to be upset and get killed because of it" excuse....and sometimes the soldier comes home and announces...oops, got a baby on the way from my time at war.