Life & Style has exclusively learned that Justin Bieber is still a toxic presence in Selena Gomez's life despite the fact that they haven't hooked up in months.

Sources say the brunette beauty got so wrapped up in her ex's personal life over the summer that it prompted her three-month rehab stay.

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“She was stalking Justin on social media,” an insider reveals. “She would drink a lot and could barely do anything but talk or think about Justin.”

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The former couple packed on the PDA during a beach trip in 2011.

Selena started bombarding her friends with photos of the duo from the beginning of their relationship even though he was dating Sofia Richie at the time.

“It was creepy,” the insider admits. “She wouldn’t stop. She said she missed him and the pictures made her happy. But her friends thought it just made her look sick.”

For more on Selena’s downward spiral, pick up the latest issue of Life & Style, on newsstands now! And scroll through the gallery below for a look back at Justin’s complicated dating history.