Mischa Barton can't handle life after "The O.C."

Life after "The O.C." isn't as sweet as it seems. Since her character Marissa Cooper was killed off at the end of last season, Mischa Barton has been dealing with some serious depression, reports gossip Janet Charlton.

A source close to the 20-year-old actress said, "Mischa is miserable since she left 'the O.C.' She feels like her life is over and everything is going downhill...She acts like she has nothing to live for."

Barton's romance with musician Cisco Adler has been suffering because of her sour mood. The insider said, "She feels lost...and started pestering her boyfriend Cisco Adler for a commitment. She threatened to leave if he didn't give her a ring. He wasn't ready to get engaged so he stalled by buying her a "promise" ring. That satisfied her for a few weeks, but she started acting crazy and hyper-emotional."

The situation provoked Adler to ask Barton for some time off, which made Barton even more upset. Charlton claims that Mischa "threatened to commit suicide and even threatened to kill their dog!" The threats seemed to work on Cisco who is now "pretending to work things out with her so he can let her down easy. He's hoping she'll come to her senses and won't do anything violent or vindictive. But he wants out," says the source.