For the first time in my life, I feel completely alone, and hopelessly lost.
Feel alone - pray, go to a park/shopping/library, get on the phone a call a old buddy, do you have a dog (there's a reason they are called Man's best friend)?
It's not hopeless, you feel lost because you never thought you would be in this situation. You don't know how to cope with it yet. That's going to change now.
How do you get a addict off drugs? Cut off all use. Time to set some boundaries. "Wife, I have decided I will not share you with another man. There will be no more contact of any kind. We will have complete transparency in this, full access to e-mail and phones. You will also remove any item that was his from our home. I will not be or our family disrespected any longer. If you do have more contact I will pack your bags and you will leave our home."
Use your military training and experience to help you. The boundaries are required to bust the affair and for you to get some sanity back. This is not a discussion, the boundary states what you need, gives her a choice in how she behaves and lays out the consequences for violating the boundary. It won't push her away, she will spew all over you verbally but don't engage that, this is about her behavior, and it will actually make you more attractive in her eyes. This move exudes confidence, clarity, strength and honor.
You can handle it.
Coach
M22,H45,W45 S21/18D12 Retain faith that you will prevail in the end, regardless of the difficulties and at the same time confront the most brutal facts of your current reality, whatever they might be.