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Lauren Conrad And Heidi Montag, The Hills
The two major stars had a major falling out when Heidi decided she wanted to move in with her boyfriend, Spencer Pratt. Lauren believed he wasn't good for her friend, and so she cut her off as a response — which was a pretty backwards way of showing her pal that she loved her.

Then again, Spencer was spreading rumors about Lauren as retribution — even going as far as saying she had a sex tape — and Heidi never stepped in to say anything. This wasn't what an ideal relationship looked like.