Has Yuuer maybe given stronger signals to Hewen than we could see?
Just reflecting it does not make sense that a person like Yueer who strongly and openly talks about all her emotions only gave signals to Hewen in the final about her changed emotions. Looking back at past seasons there were material held back that helped understand decisions that were just published weeks later. Tencent milks the show as long as possible and can publish extra material till November and they want people to be invested as long as possible.
With this premise 8.2 becomes even more suspicious to me. In 8.1 Yueer gave a positive signal to Xilun after the beach date. The next say they interact as a group and Hewen is really caring about her and in the evening he want a talk with her. Than we only see 5 minutes of a really long talk that lastet two hours. We can see Yueer less flirty and more serious than ever before, but we are not really shown her sentences. We mostly see Hewens message that Yueer is still his focus and that it never changed.
If we ask ourself, why Hewen see the necessarily to say such things, one possible explanation is that Yueer at least signaled him that at the moment her earlier strong feelings toward him are not there anymore. She does not need to say that her decision is final and she can totally open a small backdoor that they can come back.
After that honest long talk we see her coming back and crying over Xilun's letter that had no real serious content. If you consider her crying in 8.2 in Xilun's arms the tells him she cried because she sees him crying. So in this state Xilun's well-being already is connected to Yueers well-being.
From Hewen's reactions I don't get the feeling, that Yueer's final decision came as a big surprise. He wanted to stay true to his feelings, but did not expect Yueer to choose him. He already could see how Yueer behaved around Xilun the whole time and he showed respect towards both Xilun and Yueer.
So my thesis is that the production chose ambiguous scenes and left the triangle way longer open than the reality. Maybe Yueer was already 80% sure about Xilun, but if you favor her with Hewen you can still see mostly positive moments and can think she is more inclined to Hewen. That does not make her decision final, because she still had strong emotions to Hewen in the beginning and does not want to exclude the possibility of them coming back. She analyzed her emotions constantly trying to rationalize them with psychology and is really guarded. She only wants to enter a relationship when she is really sure.
The setting, dating show, not much sleep, set events, not much alone time to understand your own emotions and analyze them make it even harder for overthinkers.
So, just maybe, the strong critic towards Yueer may be a bit unfair and too extreme and we should wait for every released content, before judging if Yueer behaved unfair?