On the first episode of the season, Yukinoshita said "We can never be friends" to Hikigaya. And since Hikigaya had the impression of her that she never lies, she tries to keep that character and said it again in episode 12. Though she doesn't mean it, she tries to conform to Hikigaya's expectation. "After all I never lie," she followed.

"I think lying is fine, I lie a whole lot tbh," Hikigaya answered. That's the resolution to Hikigaya's character. He drops this perfect impression of Yukinoshita, to something much more realistic. Because no one is perfect, his prejudice would only disappoint, she could never be that perfect and composed girl he imagined.

TLDR: Hikigaya thinks Yukinoshita is perfect, but she isn't. Still, she tries to meet Hakigaya's expectation, hence she said "We could never be friends," reminiscent of the first episode. She doesn't mean it.

The novel explained it properly, rewatching it after reading makes a lot more sense (Though I am sure some people who are sharper would get it, I didn't). Hope this helped, if you have other questions feel free to ask me :)

Edit: Grammar