My cousin is a Marine. He has been released from the mandatory psych analysis long ago, but I feel like they made a mistake. He's....losing it.
I just saw him. His pride for the Marines is the only thing keeping him sane. He pulls out his knife in public and waves it around, he constantly says he's going to beat or kill people. I think he....needs more help. I'm not going to be the one to convince him (he doesn't listen to me) and my aunt is afraid to approach it, plus she thinks since he was released it's ok. I feel like he needs help. Who can I get to help him? Like...a c.o. or a friend? his friend that I do know says "it's normal" but I really disagree! How can I help him?

:bump ?

That doesn't sound normal to me. It sounds like he's still dealing with a lot of issues, and probably really feels nervous in public, etc.
There are any number of places that can help him, but I don't think that's what you're asking for here.
I'd go to this website: http://www.mc-network.de/index.html and contact the men in charge. They're excellent. They've seen situations like this before and will definitely know what to do or at least be able to get you in touch with someone with more experience. I have interacted with these men personally; they really are very skilled and they want to help.