When news broke last week that Kirsten Dunst had checked into rehab, fans were surprised because she is a respected Hollywood vet, but those who knew her were familiar with her partying ways.

Some Dunst pals even suspect her 2005 split from three-year beau Jake Gyllenhaal led to her wild ways.

“Jake was turned off by all the partying,” a source tells Us Weekly in its latest issue. (Dunst’s rep says that is “downright wrong.”)

Ironically, multiple sources told Us that regret over the breakup led her to party more – and use cocaine and alcohol. (Counters her rep, “She is not being treated for cocaine or any drug.”)

“Whenever the cast and crew were out, she was the center of the group – doing shots and encouraging everyone to drink,” a source on her upcoming movie How to Lose Friends & Alienate People told Us. “There was no such thing as ‘just the one’ for her.”

Dunst will remain at the Cirque Lodge Treatment Center in Utah “as long as she needs,” a pal told Us.

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