So did Vesper actually stop wearing the necklace because she actually cared about Bond?  Or more likely that it was part of her con to convince James everything was peachy and to not mind her stealing his/the UK government’s gambling winnings?

It’s ridiculous how cold-hearted Vesper ended up being in Casino Royale.  She’s probably the most manipulative person Bond has every come across, and it just so happens she was his lover.  Ouch!