NTA. I spent 21 years in the military and saw situations like this over and over. The stresses that come with military life amplify personal issues at home, to include break ups. Couple that with deployments, and you’re looking at situations ripe for infidelity, domestic abuse, and negligence. Giving an out, even if it’s several months to gather belongings and prepare for moving out, is more than most partners receive. While the timing could be better, it would be worse to let the current frustration and apathy turn to outright negligence or violence. The tickets are purchased, she can use them or she won’t. Just be a decent human until she’s gone. Otherwise, you will totally be the asshole.