A source tells HollywoodLife.com that Taylor was not the inspiration for Harry's song, explaining, "It is not [about Haylor], it's just coincidence."
The insider added, "Harry wrote the song with Alex & Sierra on his mind and what he saw in their relationship, not Taylor. He doesn't want to extend the whole Taylor Swift thing, he's past that whole ordeal and wants people to move on."
The source also explained how Harry and Alex & Sierra joined forces, courtesy of Simon Cowell, who "was eager for them [Alex, Sierra and 1D] to all work together after Alex & Sierra won the show [X Factor], especially since one of Alex & Sierra's best performances was a One Direction song."
While we're speculating who he wrote "I Love You" about, check out the song Harry wrote with Gavin DeGraw, called "Not Our Fault," which also has some Haylor-ish lyrics.