What did 'the dirty dead' note mean? Does he plan on killing him after raping him 19 times...

You COUNTED how many times he got fuck'n raped? Lol

I literally says it in the story.

so the uke raped him 19 times in da past and then the seme revenge on him n gonna rape him 19 times also ? is it? or someone else raped the seme in da past? urgh

Yeah something like that, idk whether the uke actually raped him though or if he just had sex with him, I haven't read the raws

I think it's probably "the dirty deed"...

That would make sense