Tay and All American Rejects front man Tyson Ritter apparently cozied up in December 2011 just after her split from Jake Gyllenhaal. This seems to be partially confirmed by his bands performance of of a mash up of their song Gives You Hell and Swift's Mean. He also said in an interview in March 2012 that he would like to record with her. The two had a casual relationship that allegedly ended because Ritter couldn't cope with Taylor's celebrity status.
Sources: 1, 2, 3, 4