XL knows because she was able to lure Fie Fie (the cute rabbit that got eaten in the beginning.) TSJ knows because…
She blushed when she saw TSJ's naked torso. TSJ is unable to tell if she is a female due to XY's magic but he knows by instinct she is a woman when she blushes.
Another hint is when XY teases TSJ in Episode 6 if he is also wanting a wife. His eyes show his desire for XY which make XY blush again.
XL senses her gender because he hears her singing while she is baiting Fei Fei. Fei Fei appears so he gets the hint due to FF's animal instinct.
In the novel, Xiao Yao says to Cang Xuan: "I just can't trust that a person who is cruel to everyone else can…
TSJ worships XY because she gives him hope to live on when she saved him. She is the only person who doesn't care how he looks like but treats him like a normal human being unlike the rest of the women he has encountered in the past.
FFYY doesn't even like him because he is crippled and has so many body scars on him.
When he has nothing, XY is there for him.
When he failed to protect her from Chang Xuan's attack in the village, he regretted his action and vowed he would never hurt her feelings.
Another hint is when XY teases TSJ in Episode 6 if he is also wanting a wife. His eyes show his desire for XY which make XY blush again.
XL senses her gender because he hears her singing while she is baiting Fei Fei. Fei Fei appears so he gets the hint due to FF's animal instinct.
FFYY doesn't even like him because he is crippled and has so many body scars on him.
When he has nothing, XY is there for him.
When he failed to protect her from Chang Xuan's attack in the village, he regretted his action and vowed he would never hurt her feelings.
So, TSJ will always be XT's first choice.
He loves her dearly but he knows she is forever lost to him. This is the saddest part of the novel.