Ideas on this book idea

I had this idea randomly and I suddenly had the immediate urge to write it out, I haven't written lately so I'm not sure if I should do this or not.

Title: unknown

He likes her so much so he approaches her every chance he gets, but she's as equally infatuated with him but avoids him like the plague because she can't trust her self around him.

Oh and he's an unhinged hitman who kills people, he goes by a nickname and it's feared by everyone. He doesn't want to tell her because he thinks she's soft and fluffy and should be protected at all cost.

But she's secretly a psychopath who's stalked him for a long time so she clearly knows that he's a hitman but lets him believe she's soft.

So basically two unhinged people madly in love but tries to tone it down for the other lmao HAHAHAHA, I was thinking slow burn rom-com thing but could also go very dark very quickly.

if this book or a similar plot is already written please point me in the direction of that book, I'm begging.