hough I believe that Sherlock lied to John about being a fraud because he really did want to break John's faith in him - because if John believed that Sherlock had lied to him all along he wouldn't grieve at his death. I really believe that Sherlock wanted to spare John the grief it's clear he knew John would feel.

If that's the case, it shows Sherlock's lack of understanding of emotions. If he'd succeeded in making John believe him a fraud, it wouldn't have turned John's grief off like a faucet. I imagine John would have felt angry, betrayed, but nevertheless still grieving for the friendship that made John feel alive again.

Then again, emotions never were Sherlock's area of expertise, so it's a mistake he might reasonably make. I suppose you're right. It just broke my heart even worse to have Sherlock telling John that all they did together, everything that John believed in, was a lie.