Somehow, I feel like Jasper should've been baffled by Stevonnie instead of disgusted by her, given the fact that it was impossible for a gem to fuse with a human.
Scenario:
Jasper: "What? You fused?"
Stevonnie: "Whoa! I ... I did!"
Jasper: "But ... but that's impossible! No Gem could fuse with an inferior organic being such as humans! It's a trick. I bet you have no strength at all!"
Stevonnie: "Well, you're about to find out!"