Justin allegedly treated Taylor's friend Selena Gomez like crap while they dated. Remember, Taylor once made a grossed-out face when she saw Justin and Selena kissing:
Also, after Taylor won the award for female artist of the year, she thanked her boyfriend, referring to him as "Adam." (Adam Wiles, a dj who is dating Taylor Swift, changed his stage name to Calvin Harris to sound more racially ambiguous.)
I'm so glad Taylor gave Adam a happy ending.