Tang Yuxin suddenly remembered that Lin Yile indeed had asked her for something, claiming it was for a "little sister" who had married early but whose husband was not good in a certain respect.
Later, when she asked again, Lin Yile refused to tell her.
At that time, as Lin Yile spoke with a blushed face, Tang Yuxin did not doubt her at all and gave her the medicine. Of course, she never inquired afterward, and she had long forgotten about the incident.
Now, she finally understood that Lin Yile had used that medicine to put Gu Qing to sleep.
Tang Yuxin guessed correctly at her first attempt,
which surely made Lin Yile feel ashamed.
Yes, one could say that she slept with Gu Qing, or rather, she had taken advantage of Gu Qing while he was vulnerable due to his grave injuries. As a result, he often remained unconscious, and Tang Yuxin's medicine worked like a charm—effective immediately—and then it happened.