After spending three months in rehab earlier this year, sources reveal to Life & Style that Selena Gomez's complicated history with Justin Bieber is partly to blame for her downward spiral.

"While Selena does suffer from lupus and other health issues, that's not the reason she went to rehab," an insider shares. "Her biggest addiction is Justin."

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Her relationship with the 22-year-old led to problems with drinking and partying after they first got together in late 2010.

justin bieber selena gomez

"She became a different person around him," says the source. "She was extremely jealous and possessive and felt like she had to keep up with him to keep him. So she would drink and smoke, and then she got into weed and partying."

For more on Selena’s rough 2016, pick up the latest issue of Life & Style, on newsstands now! And scroll through the gallery below for a look back at Justin’s dating history.