Niki was never so moody, aggressive and cold towards you considering you're his girlfriend until now. He just suddenly changed and you didn't know why

Right now, you wanted to go out with Niki and hang out with him at least once a month since it's been so long ever since you two did but instead, it ended up with him yelling at you after you tried convincing him, "didn't I told you no already? Why can't you understand that I can't give you the attention you want everytime? I mean, what's so hard about understanding a 'no'?!"