There is something wrong with what you said, MC and ML literally dated and were happy, juheon did not mind his facial expression literally at all.The only time juheon wasn’t able to “read” his expression, was when he found out he only got with him for book character or something, in which he wanted an EXPLANATION, which he had every right to want.
In what scenario was the mc not able to understand juheons emotions? He understood juheon well, the only time he didn’t was when juheon himself was emotional since he just found out the man he loved used him, so he said “don’t talk to me if you had one ounce of love for me,” or something like that. Which had nothing to do with the MC being autistic, but the ml being hurt and emotional about being used. The MC took it literally (which every person would do because duh, a man told you to leave him alone).
He then told juheon a heartfelt confession, which wasn’t enough and juheon left.

Looks like our seme cant date someone with Neurodevelopmental conditions.