The only thing that's slow-burn here is them actual realization of their feelings for each other, because there's no doubt that they like each other. You Yu checking up on Chi Tang when she's sick. You Yu telling Chi Tang she doesn't have to study because she'll get a good job and take care of her. The way You Yu can casually sleep on Chi Tang's bed, even though it's known Chi Tang doesn't like people going near her space. The way Chi Tang is extremely considerate of You Yu. The glasses, the underwear, the shower thing. She didn't even want You Yu to strain herself carrying her. The small gestures is why I love slow-burn like this.
And sure, you can construe that as things that are done by good friends, and in real life, that's true to an extent. However, yhis is a fictional romance story, and we know that simply isn't the case.