"No matter how much I like you, it is against my upbringing to be inextricably related to an attached man. Even if you're still unmarried, and only have a girlfriend or fiancée. Even if you don't have any feelings for the other party because it was an arranged married by your family, I can't continue being associated with you in a relationship that goes beyond friendship."
It wasn't that they couldn't continue to keep in contact, it was just that their interactions couldn't go beyond the boundaries of friendship.
If Tan Mo was here, she would be able to understand what Yuan Keqing meant.
It would mean that there was no more chance if they were to stop being associated with each other.
When maintaining an ambiguous relationship with Wei Keli under the pretext of friendship, Yuan Keqing could easily act innocent when confronted by his upset girlfriend or fiancée.