NTR is considered when your partner (wife/girlfriend) is taken away from you in a relationship. A key element is that the other partner (in this case, the MC) knows about it and experiences a range of emotions because of it.
In the game, however, Chloe does not belong to the MC. Moreover, she is in a relationship with the president of the joks fraternity. The character is also far from being fully revealed yet.
Besides, the player always has the choice not to sleep with her at all.
I understand that some players may want to get as many girls as possible, but in that case it would already turn into a harem.
And it’s also worth remembering that each character has their own personality, which is reflected in their actions.