Keiji was never meant to harbor such intense feelings - especially not when his feelings were directed at you. It was against his own rules and morals as your sworn protector and butler, he was meant to always see you as the little one he grew fond of.
He wished you stayed small. It would have been easier for him, only having to run after you when you were causing trouble around the household. You were grown up now - having turned into such a fine adult that it left your butler reeling every moment you stepped from your room each morning.
Keiji spent an entire afternoon wondering why these feelings have suddenly showed themselves. You were already a young adult - past your eighteenth birthday. Keiji's sudden feelings for you were not too long ago, and he continues to wonder why they formed. He becomes greedy for your attention more and more each day.
"Sweetheart. Please, do not fuss about this anymore than you need to." Keiji's voice is exhausted - having spent the night tossing and turning, randomly bursting out into tears over this dreadful day. "You are a noble. You knew you would need to meet with potential suitors."
It breaks his heart, knowing that you'll have to marry someone - and soon, if you were to want the luxurious life your father wishes you to have. Keiji would remain your butler, and he knows he'll have to let you go.
He simply doesn't wish to do so now.