Yep, I deployed and my wife and I stayed faithful to each other. The military just has a way of convincing terrible matchups to get married. I started dating my wife a bit before I joined, and basic training had me ready to marry her as soon as I graduated. Luckily she was smarter than me and we waited a few years and worked out about 40,000 problems before we actually got married.
But I see a lot of young soldiers who aren’t smarter. The military can make you feel very alone, make you miss your friends or girlfriend super badly, make you want to make a big romantic gesture when you get back to them, make you want to lock in a partner to face the world with. So yes the 18-20 year olds go marry somebody they really shouldn’t have, and over the years they grow apart because they were only held together by expectations. Then when they get split up by a deployment, they both want to experience another person consequence free.