The relationship between Isabelle Claud and Gabriel Wyatt was never much of a deep one. It was merely a business relationship between a boss and a secretary. Gabriel trusted his secretary, Isabelle, far more than he trusted his own family members. Isabelle was the ideal secretary. She would get everything done within a given amount of time. Working under Gabriel for a good five years, the both of them had developed a bond of trust and friendship. But it was never beyond that.
So when Gabriel is told by his father that the company is to be located to another city, Gabriel had naturally expected Isabelle to follow him in this movement. But his expectations are easily shattered when Isabelle refuses to accompany him which causes something inside Gabriel to snap. The thought of Isabelle being afar from him doesn't sit right with him and so, a side of him appears that even he didn't know existed.