...Is it because she parties too much

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In an interview yesterday, DEMI LOVATO was asked about her current relationship with MILEY CYRUS . . . and she stuttered a little before admitting that they're not really friends anymore.


She said, quote, "Um . . . yeah . . . that, um . . . we're, we're like . . . We're acquaintances.  It's life, and people change.  I don't have anything in common with her anymore.  I wish her the best."

We all know that Demi is sober now, and Miley isn't . . . and E! Online suggests that's why they've grown apart.

A source says, quote, "Miley is a wild card and Demi has made a point of not surrounding herself with people [who party too much]."

The source adds that they were both at a "small gathering" recently and didn't even acknowledge each other . . . quote, "It was super-awkward . . . They didn't speak, they didn't even make eye contact."