I can't speak to Vietnam, but I know a lot of people (myself included) who volunteered for OEF deployments because of home station stupidity. Ideally, when you're deployed you have your mission. You show up to your briefings, you do what you do (fly your mission, conduct your patrol, whatever), hopefully you come back safe and sound and you waste time in the rec center, the gym, or your room. Go to bed, wake up, repeat. Meanwhile, the guys are home are buried under reams of paperwork, doing 200 meters of lunges at 6 am, planning mandatory parties that almost nobody enjoys, dealing with inspections, and spending probably 8 hours per week clicking through computer-based-training modules on how to apply a tourniquet or that writing your email password on a sticky note and putting it on your monitor is bad. Send me to the desert!
A lot of military marriages are just terrible anyway. Often neither party has any idea what they're getting into. Infidelity is common, domestic violence...I wouldn't call it common from what I saw, but it happens. One of my troops was hospitalized after what was probably an altercation with his ex-wife (they were still sort-of-together-ish).
As far as an officer's leadership, I would not make a judgement based solely on him throwing away his marriage as you describe (I've never read the book, so I have no further information). He might be a dickweek commander, or he might just have been at that point, or THEY might just have been at that point. Military life puts a lot of strain on the best of marriages.