It's one of the ones that always comes to mind for me! NGL, the first time I read P&P, I was a kid and the cousin marriage really made me go "???" LOL

I haven't watched The Flash (though it's on my long to watch list) but that's the vibe I always got too. I never thought they saw each other as siblings - just best friends who grew up in the same house (and as you said, he always had a crush). But I just threw that out there because it is an argument I have seen (though again, I don't agree with it).