I don't think Harold was. The way Taylor describes it herself (RS article) doesn't seem very serious. And if I weren't on mobile, I would provide gifs of Louis shading their relationship
Taylor talked about the relationship in her video about OOTW.
Remember her last appearance on letterman he asked her to write a song about him? I hope she has at least a little snippet or something about him oct 28th when she's interviewed. Thatd be awesome