So Mai has this power that allows Sunny to be with her anytime anywhere she wishes by crossing through a magical barrier. Since he is an ER physician, he was not happy that she used them when he was currently treating patients. So she's questioning whether he really cared about his career or is it because he no longer cares about her. Her young friend told her to go with her heart. Somehow he also got the power (the pink meteorite that hit him)? This part was confusing.
Anyways, the EMT girl also likes Sunny and she decided to go after him. Mai started to feel more insecure. (Stupidly) she made it seem like he had to choose (her or his patients/career) so he said to her "please dont ask me to choose because you know i cant choose you" (I understand him with this one cus many times where i do leave my dinner date early for an emergency evaluation).
So this young friend asked her, ever asked yourself why you like me.
Sunny said "it's been 15 years, if it is it would have been long ago)
Seems like Bank's sister was killed and the young friend of Mai was the one who treated her?