Don't the Hills girls ever meet anyone new?

PHOTOS: Most memorable Hills moments

Holly Montag, 27, is the latest alum of the MTV hit to give romance a chance with former costar Justin "Bobby" Brescia, 29 -- the same commitmentphobe who once courted Audrina Patridge, 25, and Kristin Cavallari, 24.

VIDEO: Justin Bobby tells Audrina she's "better" than Kristin

"They're dating and have been for awhile," a source tells Us Weekly (on stands now).

PHOTOS: Kristin Cavallari's best bikini moments

But another insider doesn't have as much faith in the relationship between Brescia and Heidi Montag's estranged sister. "He's reckless and will disappear in his house for days at a time," the source says. "He's not reliable."

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