This will be answered in a few chapters later but if you reallt want to know
Spoiler
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He genuinely cares for the real her(Seo Urie) like the soul that went in Charlotte's body because he found the one person who is willing to love him for who he is. He is just waiting for her to tell him who she really or her true name.
https://tkor.run/%EA%B7%B8_%EC%95%84%EA%B0%80%EC%94%A8%EC%9D%98_%EC%A7%91%EC%82%AC%EB%8B%98_18%ED%99%94.html
SPOILER
The explanation goes from chapter 18-19
This is the webtoon raws, I had it MTLed in my laptop. Basically this explains how he grew to care for the real her from the moment he found out the truth.

Lancelot is so beautiful that I want to cry but he knows she is not the real Charlotte so... he pretends or?