It wasn't that Xiu had any doubts about Dylan's feelings. But she was still insisting to know what Dylan had to say. He had to have a clear view of what his own feelings were. Blindly trudging through this wasn't gonna end well for anyone.
In the case of Xiu and Darren, they both didn't know what were feelings they had for each other but they knew they had an attraction, a cosmic pull that was binding them together. But it was different for Dylan since Cali had clearly stated her feelings for him. While he was still uncertain about what he felt for her. He was still unable to give a name to his possessiveness, jealousy, and the feelings she evoked in his heart.
Hearing Xiu's question, Dylan was in deep thought. If she asked this question before he certainly wouldn't know what to say. But that kiss had only not only brought about feelings, it also brought clarity to him. A clarity he needed right now.
