The original doesn't fit Yugami's character at all. The one guy who is dead honest and direct suddenly creates some convoluted scheme where he starts working as a pizza delivery man with some light stalking on the side and then-wqtui29tj2th23g03hjgiegergkrdgdfdfd when push comes to shove he can barely manage "let's be together... but not as friends haha title drop"
Err I don't see it that way at all? I think there's an unnecessary separation between "Yugami's relationship with Chihiro post-graduation" and "Yugami's personality."
Yugami being a bit of a hypocrite
(for the lack of a better word) isn't new nor is it limited to being with Chihiro.
On Chapter 14-15 Yugami got handed the responsibility of suddenly taking care of someone else's dog. Then when the dog is finally returned to their owner, he said "I'm feeling relieved" and implied that he wants nothing to do with the dog anymore, but at the same time he looks dejected and somewhat depressed. And Chapter 21.5 showed us that he's been visiting the dog regularly and that he had been really missed the dog all this time.
That's just one of the many examples of Yugami not following his own rules and words to the letter, and that's part of his character. His reluctance to just go out and say "I like you" to Chihiro at the end of the series is 100% fitting. He may be steadfast on his own rules and says that he truly doesn't care about other people, but he still doesn't like doing the stuff that are outside of his comfort zone.
On Chapter 73 he gave Chihiro a thank you gift and tried to say "Thank You" to her but got interrupted by the fireworks, and he didn't repeat what he said because he was too embarrassed. On Chapter 79 he almost accidentally cut ties with Chihiro and his way of making amends was still indirect.