Dean threw away his necklace for several reasons. Firstly, after their visit to Heaven, Castiel returned the necklace to Dean, stating that it was “worthless.” This statement from Castiel may have influenced Dean’s decision to discard the amulet. Dean has always valued the opinions of his angelic friend, and if Castiel deemed the necklace to be worthless, Dean may have believed it to be true as well.
Secondly, Dean may have been feeling disillusioned and hurt after seeing Sam’s “happy memories” in Heaven. These memories were largely ones in which Sam was away from Dean, enjoying a life without the burden of hunting. This may have made Dean feel like an outsider in Sam’s life and caused him to question the significance of their bond. In this state of emotional vulnerability, Dean may have seen the necklace as a symbol of their relationship and decided to discard it as a way of distancing himself from the pain he was feeling.
Additionally, the necklace held sentimental value for Dean. It was given to him by Sam as a symbol of their brotherly bond, and Dean wore it constantly throughout the show. However, Dean may have felt that the necklace no longer represented their relationship as it once did. The events in Heaven and his feelings of isolation may have caused Dean to associate the necklace with negative emotions, prompting him to get rid of it.
Furthermore, Dean has often been portrayed as someone who carries the weight of the world on his shoulders. He may have viewed the necklace as a tangible reminder of the burdens he has carried throughout his life, including the responsibility of protecting Sam. By discarding the necklace, Dean may have been attempting to let go of these burdens and find a sense of freedom or release.
Dean threw away his necklace for multiple reasons. Castiel’s statement about its worthlessness, Dean’s feelings of disillusionment and hurt, the necklace’s sentimental significance, and Dean’s desire to let go of his burdens all likely played a role in his decision.