I would be more ok with discussing the history of the diamond if they had made it clear in flashbacks that Regina didn’t fully expect to win with the Curse. She may not trust Rumple but she did trust the Curse. The first line she says when she wakes up in SB is “I’ve won!” And then suddenly two episodes later she was all, “oh yeah, I have this backup plan stashed away in case the Curse didn’t work.” I need to be able to follow that train of thought and the way they’ve characterized Regina doesn’t allow me to believe that she thought of a backup plan. Heck, nothing she did including the Curse was her own idea.
Now, if they show me in flashbacks that she got the diamond from Tink (though I still don’t know what she would trade) then maybe I’ll revisit this.
As to PP being lonely: but he let Wendy go and that doesn’t explain why he wants Henry so badly.
As to Regina trading kids for the diamond: Regina’s relationship with kids is complicated. She has, as we’ve seen, capacity to care for them greatly (Henry, Owen). Even if she separated Hansel and Gretal from their father, she also offered them life with her because in her own way she came to care for them. She may be ruthless in her quest to kill Snow but would she banish a bunch of scared little boys to life on a nasty island with PP? I don’t know. I really don’t.