Making her choice was easy; living with it isn't (anime-based).
It was as easy to hate Alucard for offering her a choice as it would have been to despise him for denying her one. It had been her choice, but she hadn't known--hadn't thought beyond her love for the blood in her veins, and the breath at her lips. She had made her choice, but wasn't fair that she pay so high a price for her own life.
Not fair, not fair at all.
"Life isn't easy, and it isn't fair," her commander had once said--but he had never faced a bowl of human blood with such hunger gnawing at his gut. The blood had been freely given, without the taint of violence and terror (she knew the scent of both, knew that blood spilt in battle, during the hunt smelt rich, exhilarating). She was hungry, always hungry, and the blood was there--
She had wanted to live, but she had never once imagined that life was possible without her humanity. She had made her choice, blindly, desperately, and Seras Victoria would not make the same mistake again. She had dedicated herself to protecting the innocent, and doing the right thing. She wouldn't let herself become a monster in order to make things easier for herself.
Monsters were born from the most humble of origins. That the blood before her made her belly ache and her mouth water made Seras enough of a monster already.
She had been strong her entire life, even stronger than she sometimes wanted to be. She would be strong now. Anything less was not worth her life. Anything less was damnation for loving her life more than fearing the demon she had given herself to.
She poured the blood into the sink, and closed her eyes against the sight of it draining away. She was strong, human still--and her hands shook, and her stomach ached with hunger.