first of all, she randomly saw him in an elevator and says she was screaming on the inside but didn't actually speak. and then saw him shortly after at an afterparty and decided to approach him. so she ALWAYS liked him.
she tried to create a "fantasy" and when she couldn't make that fantasy a reality she decides to post a monetized video to play the heartbroken victim and paint michael out to be the bad guy - on his birthday at that.
their relationship started off as business transaction initiated by nikita to do these fake boyfriend videos, model in her campaigns, etc. i think her initial crush on him combined with the image of them being together, her fans speculating and shipping them, and the fact that nikita gets her validation from situations like this intensified her feelings for michael and really gassed her up to make things real.
being as though the relationship was transactional from the beginning and nikita initiated the whole thing...michael really didn't do anything wrong. he was supposed to get something out of the whole situation. he played the role nikita hired him to play. michael didn't start off trying to date nikita. nikita approached him to fake flex for the gram so how did michael do her dirty? nikita should have kept it professional and failed to do so, so that's on her.
nikita likes presenting this image of her being desirable to straight or masculine cisgender men. having michael allowed her to perpetuate that "fantasy" to her followers. so she can miss me with all of the bullshit. and she admittedly knew there was another girl in the picture and that she wasn't "dating" michael exclusively, hell it's clear that they weren't dating at all...moreso talking. so i'm not sure why she felt michael owed her anything.
she's just like james charles using her fame and followers as a way to attract and manipulate guys and then getting upset that people don't genuinely want to be with her for her. birds of a feather...