The on-again, off-again couple is definitely on-again, and a source tells ET that Bieber isn't taking his second chance with Gomez lightly.
"Selena is 100 percent the reason Justin turned his life around," the source says, referring to his well-publicized bad boy behavior in the past. "She's the one that got him involved with church and that opened up a whole new group of friends to him too."
"Justin wants to be a better man because he doesn't want to screw things up with Selena," the source adds. "He knows he's lucky to have this second chance and he's not taking it for granted. And the truth is, this 'transformation' hasn't been all that difficult for him because he wants it."
Our source says the 23-year-old singer's priorities have definitely changed.
"It's true that you can't change someone unless they want it, and he wants it now," the source explains. "He knows what's at stake. He would way rather spend a quiet night in with Selena than go get wasted and hook up with random girls. That lifestyle just doesn't appeal to him anymore."
And Bieber's family apparently couldn't be more on-board with the rekindled romance. Our source says the "Sorry" singer's mother, Pattie Mallette, "loves Selena" and that his family believes she's a good influence on him. However, our source says that it's still taking time for Bieber to be in all of Gomez's family and friends' good graces.
"Justin really messed with Selena the first time around and she was in a bad place because of it," the source claims. "Over the years she's worked on herself and is way stronger now, but they were all still worried at first that it would all unravel if things went south. Luckily, it seems things are going really well and he is back in some of her friends' good book."
Despite some of Gomez's pals apparent feelings about Bieber, the "Wolves" singer's inner circle isn't forcing her hand one way or the other, the source adds.
"There's no way Justin is banned from coming to her family's place," the source shares. "They may not be totally on-board with the reunion, but they're not going to make her choose between family or him."
Recently, Bieber has indeed appeared to take steps to strengthen his bond with family. Last week, he posted a heartfelt message to his dad, Jeremy Bieber, about "fighting for" relationships.
"I️ love continuing to get to know my father," he wrote alongside an Instagram of the two walking side by side. "I️ love working through hard things to get to the good things... relationships are worth fighting for especially with family!! Love you forever and always daddy!"
Meanwhile, 25-year-old Gomez and Bieber were last spotted together late last month at the Montage Beverly Hills Hotel after attending a church service together. During the cozy get-together, the two shared an intimate embrace.