Okay, so I don’t normally do this, but…

Garnet said “You need a gem at the core of your being. Then you need a body that can turn into light. Then you need a partner whom you trust with that light. Literally.“ So Greg couldn’t fuse.

But Steven and Connie can fuse. Connie doesn’t have a gem, and she can’t turn into light. So… How?

When Steven shrugged off gem destabilization, it was because he’s part human. The human aspect of him keeps his body whole. That made sense. He may not even be able to retreat into gem form. With how fragile the other gems treat him, they certainly make no indication that they expect him to be able to.

But how can being part human let him to turn someone else into light? How can the same aspect that protects him from destabilization allow him to turn into light at all?