For what it's worth...
I hear a panicked cry for help, here, brother. I've never been on a sub, uh, that's not moored, so I don't know what that does to you. I've been around the military for most of my life, though, up to having a son in the Corps and helping his girlfriend through deployments. Here goes.
Take a deep breath.
When you're talking about how you feel, it could be me writing. The twisted gut, the feeling of hopelessness, the panic, the not knowing what to do. You didn't mention it, but I bet you have insomnia, too.
My wife is poly. I'm mono. I liked her having sex with other guys because it was just kinky sex. But then she realized she didn't like casual sex, she's poly. Now she's in a relationship, and has been for about five months. At first, I didn't have any trouble with it.
Then the insomnia started. She was getting attached to him. It was less fun. They talked about a threesome. They talked about wanting me involved. But I felt very left out. It was the exclusion from this important part of her life. I felt lonely and lost.
Whenever I tried talking to her I let the emotions get out of control. The anger and the hurt and the paranoia all fed on each other, and she picked up on it. My own mind (because of an insanely stressful time at work) generated all kinds of accusations and things to worry about. We fought. She went to him. I felt worse.
I would text her, but she wouldn't respond. She wouldn't console me by telling me what I wanted to hear (good for her). It left me feeling like she was hiding things. That made my feelings worse.
I felt the same way you do. I wanted her to be happy, but it hurt and I wanted her to end it. We talked about boundaries, but I didn't want to make her feel caged because of me. Things were going tango uniform, no pun intended.
Several things turned it around for us.
First, reading here helped us both to understand what was going on.
Second, we started talking when we weren't emotionally charged. That helped a lot.
Third, I accepted that her time was her time and my communication with her would be limited.
Fourth, I started hanging out with him. And him and her.
Not perfect, but things are much much better now.
If you want reassurance, I'd say the fix is a lot inside you. You're completely capable of resolving this. You have to look inside yourself and get comfortable with you.
If you want to talk privately, PM me. I want to help you out.