Karima felt relieved, but Gao Yang felt burdened.
Seeing through but not speaking about it, knowing what's going on but pretending not to know, allows two people to continue to interact. However, when a sudden situation caused Karima's long-repressed feelings to erupt, it made their interactions very torturous.
Some things, if not spoken, everyone can still be friends, but once said, even being friends isn't possible anymore.
The problem is that Gao Yang is a typical example of indecisiveness when it comes to matters of the heart. As long as things are left unsaid, he can continue to drag it out. Once he knows, or once it's pointed out, he's completely lost.
If he could make up his mind, telling Karima it's impossible and that she should give up, Gao Yang would no longer be troubled. But, Gao Yang simply can't say that, whether because he's too kind-hearted or too embarrassed; anyway, he just can't say it.
