 Why does Ben leave Laura?
And yet, at the same time, to be filled with a terrible, gnawing fear—a fear locked in my mind during the day and bursting out like an evil jack-in-the-box at night. The Academy, with its great halls and classrooms and laboratories, lay hollow and silent, an exhausted thing at sleep after spawning its first-born. Let him leave Jupiter and the others alone! 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. He was Chief Jetman now on the Lunar Lady , a commercial ore ship on a shuttle between Luna City and White Sands. 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. The Universe was mighty big, but with two of us to face it together, it would be only half as big. And you, Laura, were with him. "Ben," he called, "don't forget that offer. A moment later Mickey said, frowning, "What was he talking about, Ben? That's what most of you want, isn't it? Then your last words came back and jabbed me: "That's what Mickey used to want."
 Ben leaves Laura because the call to explore the universe is irresistible.
 Ben leaves Laura because he feels guilty that he dragged Charlie to Mickey and Laura's parents.  Ben leaves Laura because she wants kids, and he doesn't.  Ben leaves Laura because the call to explore the universe is irresistible.  Ben leaves Laura because he knows he'll grow to resent her if he stays.