In the episodes The Return and Jailbreak we find out that Garnet is a fusion between Sapphire and Ruby who had fused back when the rebellion (led by Rose Quarts) began, it was an accidental fusion but they fused, they left Homeworld and soon found Rose and Pearl and joined what we know as the Crystal Gems.
Steven and his friend Connie can actually fuse together and they together create Stevonnie. So here is the actual point of this post:
We see that non fused gems (Pearl for exapmle) is humanoid. However, fused gems look more wild (multiple arms, large sharp teeth, claws, angry looking.) They even act animalistic. Except not all fusions look or act like that. Stevonnie and Garnet look humanoid, they are essentially perfect together. They have perfect relationships. Garnet however has the third eye meaning that they aren't perfect but they are pretty close right? Stevonnie however looks totally humanoid, acts like a human and doesnt have any extra limbs or eyes. So conclusion, Steven and Connie are litterally perfect for each other.