Harry and Taylor met at the 2012 Kid's Choice awards on March 31st, 2012. It was then that they began a casual relationship. However, the relationship ended after Harry kissed Emma Ostilly while in Australia.
Over the summer, Harry dated a couple of other girls while Taylor spent some time with Conor Kennedy.
After Taylor's relationship with Conor ended, it appears that she got back together with Harry rather quickly, as they were seen out after the VMA's on September 7th 2012.
Their relationship went public when she began wearing his necklace while out in Paris in early November. Their first public date was at the Central Park there and that spiraled into a crazy December of outings in New York City, London, and Utah (where they got into a snowmobile accident). They even spent New Years Eve together and publicly brought in the new year with a kiss in Time's Square.
After New Years eve, they went on vacation together to the British v*rgin Islands, however this was cut short after they supposedly got into a massive argument and broke up, leading to Taylor leaving the islands alone.
For most of 2013, their relationship seemed to be sour with Taylor mocking Harry at the Grammy's and then again at the VMA's however, after the VMA's they attended an after party together with Ed Sheeran.
However, in 2014 it seems that they have resolved their issues and are good friends, or at least amicable. In 2014, Taylor released her album '1989' with a load of songs about Harry, all relatively good in spirit. These songs included "Style", "Out of The Woods" (in which Taylor references the necklace and the snowmobile incident), "All You Had to do Was Stay", "Wildest Dreams", "I Know Places" and "Clean" among others.
They were seen together at Caleb Followill's birthday party as well as an after party for the Victoria's Secret Fashion Show. Harry was even heard whistling after Taylor received an award at the 2014 AMA's.
In 2015, Taylor released her music video for her single about Harry called 'Style'. In this music video, she is shown holding Harry's paper airplane necklace numerous times.