The other reason is you

You, my Nathalie

As Gabriel arose from the secret layer he turned to Nathalie who had just looked up from her computer screen.
G - I'm giving up Nathalie, I know what you will say that I said this last time but I mean it.
N - but sir, you promised Emelie
G - I know but I also promised to be a good father to Adrien
N - if you change your mind I will always be here for you, but what did make you change your mind?
G - you
N - me?
Nathalie met Gabriel's eyes, she was shocked.
As she scanned his face she saw a small smile began to replace his usual stern look.
N - Sir?
She asked as one eyebrow quirked upwards
G - please call me Gabriel
He walked towards Nathalie till he was in front of her desk
N - Gabriel, What do you mean me?
G - you my, Nathalie have captivated me.
You've always been there for me, Adrien sees  you as a mother, he loves you so much and I -
I love you too my dear, Nathalie

Nathalie remained silent, she slowly arose from her chair and in one swift movement she grabbed Gabriel's tie pulling him towards her and she kissed him.

When they broke apart Nathalie placed her hand upon Gabriel's cheek
N - I love you too moi papillon, I have always loved you.
Gabriel could do nothing but smile, he pulled Nathalie in for another kiss.