LeBron James says he can't stop crying over the death of his great friend Kobe Bryant ... saying in an emotional goodbye letter, "I’m heartbroken and devastated my brother!!"
James penned the words in a lengthy social media post Monday night ... addressing Bryant's death for the first time since Mamba, his daughter Gianna and 7 other people were killed in a tragic helicopter crash Sunday.
"Man I sitting here trying to write something for this post but every time I try I begin crying again just thinking about you, niece Gigi and the friendship/bond/brotherhood we had!