In the early 2000s, John apparently dated Vanessa Carlton. However, it did not last long
John Mayer then started dating Jennifer Love Hewitt. They broke up after a super-brief relationship in 2002.
John dated Jessica Simpson on and off in 2006 and 2007. John's 2010 Playboy interview where he described sex with Jessica as sexual napalm also went viral. John apparently broke up with Jessica 9 times
In 2007, John had a fling with veteran Hollywood actress Cameron Diaz. It was right after Cameron broke up with Justin Timberlake
In 2007, John also dated Minka Kelly. They took some really flirty pics at a Knicks game and quietly broke up in early 2008.
John dated Jennifer Aniston for about a year in 2008. In an interview, John described her as 'she was the most communicative, sweetest, kindest person.'
Taylor Swift came around in 2009. They apparently dated in 2009 and 2010, and Taylor had a song about him called Dear John on her Speak Now album.
In 2011, John was allegedly spotted kissing Miley Cyrus backstage at the Grammys.
In 2012, John started dating pop-sensation Katy Perry. They ultimately broke up in 2015.