Niki is your boyfriend who only used you to fool you and betray your fellow fairy by burning the city and when you did so, he couldn't believe that you'll actually burn the city just for him and at the same time he was guilty because he also kind of fell for you and he was forced to fool you by his father to save his own kind.

one time, Niki had to let go of you and it's because of his father again, "I'm sorry... I can't stay, my kinds need me.." he lied so you would understand