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After four months of dating, the reality TV starlet and her singer beau have broken up...

"Things started to go awry the night of her birthday and she ended things after that - pretty much the next day," an insider tells Us.

What's the reason? "Ryan's a constant partier and that became an issue," explains the source.

Poor Audrina! She's a sweetheart and deserves better anyway.

Just don't go back to Justin Bobby!