The 20-year-old star told Italian network Televisionet.tv: "I ended up having to go through some stuff. Fortunately I have family and friends around me that are very very supportive of me and my recovery and everything I stand for.
"Nick especially. He's always been there for me.
"And Selena because she called me crying when I was in there and was just so worried. I was like, 'Look, I should be the one crying, it's all good!' But she was so worried and ever since then we've gotten closer."
The 'Heart Attack' hitmaker insists she is doing much better now and feels good about herself.
She said: "I have more confidence than I did a couple years ago. And to me, confidence is sexy."
The singer previously claimed that rehab showed her who her real friends were.
She said: "A couple of months before I went to rehab, I had a birthday party, and there were a couple of hundred people there. It was full of people who I considered my closest friends.
"When I turned my phone on after being in rehab for three months, I expected lots of text messages and phone calls. I had four texts. That was a wake-up call."
Demi cut most of her old pals out of her life and now only has a small support group of people she can rely on.
She said: "I don't have loads of friends. I used to, but then I realised, do any of them actually care?"