I have seen the cheating first hand. I personally have never seen anyone egg someone else on, nor have I ever been egged on. I won't say that it happens. it's just never happened around me.
the cheating happens on the spouse end too tho. I've seen many a navy wife go from the pier to the bar and take someone home with them.
pre and post deployments are hard. you have a lot of things to do before you go. it's hard on both parties. coming back, both parties have been completely independent in everything they do for several months and it takes time to get back to normal.
I'm not so sure I see poly as a completely valid approach though. I'm sure I could have found a loving relationship when I was in Italy back in 03 but I'm sure hearts would be broken when it was time to go home and I haven't been back since. maybe a fwb or maybe just the agreement between husband and wife that non mongamy is fair game.