i can see her having a really rough time moving to nyc for her first semester so maybe they bonded over that and were inappropriately close friends for a while? she can be super clingy so i can see an emotional affair brewing that he just had to put a stop to or whatever? tbh i am not sure she would be super mature/take it well at first but i think things between could be fine now? maybe they had a good talk about it her senior year over coffee