 Why does Ben tell Laura his has her wedding ring?
They're going to bring us the metals and minerals that we desperately need. My parents had died in a strato-jet crash when I was four, so I hadn't needed many of those "You are cordially invited" cards. Just one, which I'd sent to Charlie Taggart. I remembered how, as a kid, I'd pestered him in the Long Island Spaceport, tagging after him like a puppy, and how he'd grown to like me until he became father, mother, and buddy all in one to me. And you, Laura, were with him. "Ben," he called, "don't forget that offer. You kept looking at me until I had to ask: "What are you thinking, Laura?"
 Ben is telling her that even though he can't stay, she is the only woman he'll ever love.
 Ben is telling her he can't marry her, so he's taking back the ring.  Ben is telling her that even though he can't stay, she is the only woman he'll ever love.  Ben is telling her that the marriage is over, so he's taking the ring back.  Ben is telling her he was going to marry her but, she can't compete with the universe.