Why does Cassia think that she shouldn't be Matched to Xander?

Cassia's father comes to tell her that there is a message for her on the port. She destroys the napkin and goes to talk to an Official who appears on the port. He tells her that it's time to get together and do something special with her Match. She and Xander will have a special meal the next night, chaperoned by an Official. After the call, Xander comes by to visit and it feels really good to be with him. It's a different kind of good than being with Ky. She feels that she knows Xander too well to be matched with him.