Same way you ended up here? It's hard to say, but like I said, I'm pretty sure KPDs just collect their favorites. Like trading cards.
Not sure. They may tell you or they may not. I suppose it depends on what kind of history they had with you and aren't sure how well you'd take it.
It is, unfortunately, one of the largest downsides of the KPD. Friends and lovers you make will disappear and sometimes they come back but they don't often remember you, unless they were from your universe to begin with. I'd say you get used to it, but that would be a lie.
Do me a favor? If Castiel shows up, put in a good word for me? He saved my life more than once and he was dear friend to me.