John Mayer's 'Shadow Days,' a song about learning from mistakes and moving forward, is apparently a personal message to his ex, Jennifer Aniston. Us Weekly quotes a source close to Mayer who claims the actress inspired the introspective track.

"It really took him a long time to get over her. He really loved her a lot," the insider says. "He wrote the song as a farewell letter knowing [Jen] would hear it. Ultimately he's done a lot of self reflection though and he realizes they weren't right for each other."

Mayer and Aniston began dating in April of 2008 and were on-again, off-again until late 2009. In 'Shadow Days,' he sings, "Did you know that you could be wrong and swear you’re right? / Some people been known to do it all their lives / But you find yourself alone
 just like you found yourself before
 / Like I found myself in pieces
 on my hotel floor / Hard times help me see / I’m a good man with a good heart / Had a tough time, got a rough start / And I finally learned to let it go."

After dating Aniston, Jessica Simpson and Jennifer Love Hewitt, Mayer is done with celebrity romance. "He's looking for a nice, non-famous girl he can relate to," the source says. "He loved [Jen and Jessica] both but it really affected him emotionally and it wasn't worth it."