When matters of the heart are involved, its especially hard to dissolved. Its not your fault, dont drool over it.
Matters like this is best let it takes its own course, coz no matter how much you invest your effort in, it aint going to turn out the way you want it to be.
My suggestion - Said what you have to said although you will feel guilty towards your friend, but there is nothing you can do at this moment. I assume your female friend also express interest in going out with your army friend so its not entirely your fault.
Just my humble one cent worth..
