Bieber, 21, unveiled the song last month. It is the lead single of upcoming fourth studio album, which will be a follow-up to his 2012 work "Believe".
"While people were writing that I was stupid for being in (the relationship), this is what I always saw in him," Gomez, 23, said in an interview.
Talking about her own album "Revival", the star said it is about her story.
"It's all part of my story," Gomez continued of her past relationship while referring to "Revival".
"I knew deep down that this wasn't what I wanted to do - being exhausted of forcing something that wasn't right, even in my personal life. I had to have moments where I was crying and I was like, 'Why am I not in love with what I do?' I was forced to get very uncomfortable for a while in order to make the decisions I made," Gomez revealed of switching labels and management in preparation of her upcoming album.