Take away the fact that this dirt bag is "sorta/kinda/no longer" family. (He's not, right, b/c the uncle divorced his mom before he died?)

Would I be ok with my partner bringing a woman he ***** many years ago into MY house?!?!? HELLS to the N-O! That is disrespectful and I wouldn't put up with it! So they're not blood. She STILL ****** her cousin! That's like saying its OK for adopted siblings to sleep with one another! Uhm, nope, not socially acceptable!

I'd say play hard ball and start bringing around old flames of yours....but she was your first. Still, can you bring around old flames of yours (even though you didn't go all the way) and give her a dose of her own medicine? She can't say that she doesn't like it! (Ok, a bit spiteful, but she's kinda disgusting if she defends going three rounds with a cousin.....ewwwwww.)