Sources close to the former couple tell TMZ ... the exes are telling friends their on-again-off-again relationship has finally gone kaput because they've grown apart ... figuratively and quite literally.
Remember, while Nikki was filming "Total Bellas," John was tied up in China ... and that distance further fractured their already-teetering relationship.
Our Nikki sources say she also realized while watching Sunday's finale of 'TB' how unhappy she was and hated the feeling of being confused and living in a gray area. Watching that high level of uncertainty reminded her why she ultimately chose not to walk down the aisle with John, despite his pleas.
We're told Nikki doesn't regret her decision, but dating someone new is the LAST thing on her mind. She's now focusing on her career. We broke the story ... Nikki's moving out ofJohn's place and finding her own spot.