Sounds to me like "military man" isnt invested as much into the relationship as his girlfriend is. Honestly, I think I might keep my mouth shut unless girlfriend asks. I would definitely let my hubby know that I don't appreciate him being in that kind of situation either.

Sooner or later the true colors of 'military man' will come out and be there for your friend when it happens. If she would freak out if you told her, then theres no sense bringing grief upon yourself. They are both adults so let them work it out on their own.

Good luck.

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"Why must you speak, when you have nothing to say." Horatio Hornblower