The other reason is you

The truth

Gabriel had come to talk to Emelie just like any other day, except this time he was going to admit the truth.
Gabriel gently placed some flowers upon the glass coffin.
G - Emelie, Please forgive me but I can't go on anymore. Adrien needs his father but that's not why I'm asking you to forgive me. You told me to look after Adrien and find happiness and I have, Adrien makes me incredibly happy but he's slowly slipping away and Nathalie...
Gabriel couldn't finish
G - Nathalie she ... I - I love her Emelie.
I didn't mean to fall in love with her but I have.
I can't see her suffer the same fate as you my love, I will always love you but Nathalie she makes me so unbelievably happy.
I need to tell Adrien and Nathalie how much I love them before it's too late.
The people I've hurt Emelie to get you back, the list, my what a list it would be.
I've hurt Nathalie the most, I should never have let her use the peacock miraculous but she did it for, for my happiness but that's the thing, she is my happiness. I've realised that now and I can't loose her and Adrien.
He looked at Emelie, tears cascading down his cheeks.
He had to go see Nathalie.
He has to tell her.