Their relationship started when they agreed to try and discover what is going on at the Greenhouse. As they put their past feelings of irritation and hate behind them they begin to develop a friendship. Daniel eventually expresses he has feelings for Hayley, and in the last episode of Season 2 admits it to her. He kisses Hayley, leaving her torn between Leo and Daniel. But the end of the episode leaves us on a cliffhanger, so we do not know who she chooses. There is also the possibility that it is someone else.
Although, we have reason to believe that it could be Daniel at the door, as when Hayley is hanging out in her room she gets up, looks out her window and sees her family playing basketball. This causes her to text an unknown contact asking them if they wanted to drop by. The idea of basketball could have motivated Hayley to invite Daniel over. Another reason to believe it is Daniel at the door is because when the doorbell rings Hayley gives a playful smile, the same smile she gives Daniel after he pulls her in for a kiss. Also, it could be Daniel due to Daniel and Hayley unexpectedly working closely with each other throughout Season 2, over Leo and Hayley’s original dynamic in Season 1. But, there is also a chance that it could be Leo, as after she turned on her record player, she lies on her bed and first thinks of Leo, and also because earlier in the episode, Leo says that if she gets bored, she could call him anytime.