If you don't mind her having fun, and sex with her friend, then what's the problem? The more you post the more confusing it gets.

I tried putting myself in your shoes, and any way I slice it, she would be gone if she could be faithful, and loyal until I got back.

Its no different than a military wife, where the husband is gone serving his country. The wife finds ways to deal with the time, and distance in an adult mature way, or she better take the kids and get her own life.