The woman I loved was a banker and therefore a poisoner. Had I been a banker myself, loving her would've been suicide; being the bank's detective, it just made my job harder.
Being a bank detective was supposed to be a well-paid sinecure. I had been offered it because I was a very good detective, and I had accepted it because I had been tired of it. I wanted to stop caring about the victims -- the unrelenting grief and misplaced guilt that had made me loathe my job and excel at it. The same superintelligent quantum AIs that had revolutionized finance had also changed forever applied biochemistry (read: poisons), making internal competition in financial institutions more profitable, more lethal, and almost impossible to stop. Finance became the art of gaining control of the money the company computers' made, and life expectancy in the rarefied heights of the field plummeted as the order of magnitude of their wealth rose.
It was fine with me. As the bank's detective, I was not supposed to solve any murder - I was just a token gesture to insurance companies and what laughably pretends to pass as unbought law. And as a person, I couldn't care less about them. The money was a large multiple of what I had made in the outside world, and most people killed had, I knew, killed others to earn the dubious right to be poisoned as well.
I made no friends among them, not that either side would have wanted to. I slept with a couple, mostly for the heck of it. I fell in love with one, no more beautiful than the others (but all tended to be), just as smart, and just as empty-souled. Don't ask me why her - she had no redeeming qualities above the rest, and that was already a low baseline.
She was even the worst of them at killing, so bad that I could actually prove, for the first time as a bank detective, she had been the one who had killed her boss. She had been the main suspect, as usual in these cases, but for people with their resources that shouldn't have been a factor. They had supercomputers to plan their crimes, yet she had screwed up so badly that I could prove it had been her.
She wasn't afraid when she found me waiting for her in her apartment. I knew she wasn't braver than the others. Perhaps she had thought my love would protect her. Perhaps that had been her deliberate plan all along: with everybody else using sophisticated designer poisons, to fall back to older forms of chemistry.
She should have trusted the new ones. Quantum biochemistry had figured out new ways to kill more things than the human body. I had loved her, yes, but I had taken a pill for that half an hour before.
The gun in my hand was old-fashioned, though, and my function in the bank's game-theoretical theater was older almost than poison itself.
Afterwards, still sitting in front of her cooling corpse, I realized I didn't know if the pill's effect was supposed to be permanent or not.