Need help to write an erotic short story (kink friendly)

Hey,

As of now I’m deep into my new novel and got stuck with the Sex scenes in it. As for the plot (as short as possible), it’s about an intruder who leaves love letters in the apartments whenever he breaks into. A female cop then finds out every letter was directed to here. Unsure if she should follow her responsibilities as a cop or her desires as a woman she’s having a moral conflict. But we’ll, she later complies and they get naughty.
I never wrote anything related to Sex and would love any input about how to write, especially how to make it as realistic as possible.
Any messages are appreciated.

Have a nice day!