Thanks for sharing your story, sad as it is.
What immediately came to mind when you said "This wasn't my best friend. . . . this wasn't the man. . . ." is that you came face-to-face with his reacitvated cult personality which is a real and separate personality from the person you fell in love with.
Read Hassan's Combatting Cult Mind Control for a better understanding of what happened, and go from there.
Best of luck,
BOC