I just thought the whole pairing was unnecessary as they didn't use it to progress anything, but instead take a step back it seems, plus I've seen enough of Castles exes to last me a lifetime.
This. At this point, if they bring someone on the show for Castle or Beckett I just yawn. I know the steps by now, it's the same old dance over and over again. Castle is a solid show when all is said and done, but I do wish the writers would stop it with the exes and potential love interests that exist solely to inspire jealousy or point out how perfect C/B are for each other, etc. It's unnecessary and uninteresting.