Hi everyone!
I did a recap of the times the drama implies that XY loves XL and someone told me to post it here as well.
Episode 19, XY's father surprises her smiling in front of the mirror containing XL's memories. She tries to hide this from him, like a teenager caught in the act. The drama focuses on the king's astonishment that his daughter isn't pining for TSJ, the one she's supposed to love, but instead thinks of another man. XY explains she isn't a romantic and doesn't trust TSJ. If he keeps his promise, so much the better, if not, too bad. But after saying she's not a romantic, she glances embarrassed at her mirror. Which tells the audience XL is in her heart while TSJ is still just a suitor for her but hasn't won her full love & trust yet.
Later, she confesses to XL she is afraid of dreaming of him = falling in love with him (fear which is only possible if she already has romantic feelings for him).
Episode 20, she throws herself into TSJ's arms and even the latter realizes she doesn't do it out of love (= she tries to forget XL by clinging to TSJ).
Episode 22, she shows physical attraction for FFB when she first met him then when he was teaching her archery.
Episode 23, when he asked her to go wandering the world with him, she agreed on the condition he abandoned his responsability. She was sincere in her answer even though she said it with an arrogant tone since she knew he couldn't. There was a hidden bitterness.
Right before, she mentions XL as a possible husband to her grandfather, just like TSJ. Which indicates she considers the two men as potential future lovers.
Later, she touches FFB's heart, understanding he is probably XL and lets him hold and caress her hand. Her gaze screams "I have feelings for you".
Episode 25, XY has the look of a lover who languishes of her man when she unmasks the guy who has entered her room. And she seems to have hope it's XL when she asks him "are you...?" before being annoyed when she thinks it's only FFB.
Later, when she knows he is XL, she tenderly watches him sleep, thinking back to fond memories before hardening herself by remembering the pain he caused her. The lyrics of the song used at this time (which is the duet of XL & XY) literally explains her thoughts: she wishes she could be with him in a next life but in this one, she feels torn while being afraid of losing him.
Episode 27, she calls him her soulmate and wishes he was only living as FFB and not XL, the enemy of her family. She then watches him leave with so much sadness and regret.
Episode 32, when she wakes up but XL refuses to see her, her attitude, her tears and the song used literally confess her love for him, a love that she can never express and that he never lets her express.
Episode 33, when XY tells her cousin she is going to wait for TSJ, CX is surprised because he has never seen her waiting for anyone and deduces that TSJ is really special for her. At that moment, the camera focuses on XY who is making a weird sad face because there is someone she keeps waiting for: XL. She waits for him to confess to her, she waits for him to come back, she says goodbye to him every time they see each other because she doesn't know if he won't die in battle etc... Almost all their scenes since she's the princess of Haoling are goodbyes.
Episode 34 screams XY loves XL. Her reaction when he calls her name at TSJ's house is that of a hurt lover, not a friend. Then, when XL mentions how the young slave was able to survive for 40 years, talking about following his heart, being patient and not giving up a faint hope, XY turns to him apprehensively, tremolos in her voice and a look that indicates she imagines XL is telling her not to give up hope they will ever be together.
Then the drama clearly shows that XY's desire to see the young slave won, her joy at his victory and her empathy afterwards are increased tenfold because she draws a parallel with XL and thinks of the latter. Which is shown when she tearfully tells him she wished she had saved him from the arena so he wouldn't owe anyone anything and could live a free life where he wouldn't be the enemy of her family and wouldn't have a losing battle as his destiny. When XL, moved, reaches out to caress her cheek, XY doesn't move and even has eyes filled with emotion. This scene alone proves they both love each other but cannot clearly express their love because of the political situation in which they are. They can only be best friends. Even TSJ is aware of this as XY lets go of his hand, lost in her thoughts/emotions towards XL.
There is also the fact she sent him poison every month, before discovering he was FFB and next to her, the fact she always walks around with poison for him etc... (which indicates he constantly occupies her thoughts).