Demi Lovato opens up about Alex Welch and Joe Jonas in the latest issue of Elle

“I was completely out of line all summer. Just the worst attitude – totally ungrateful … I just felt like she’d betrayed me. That’s the bottom line. When you punch someone on a plane, enough is enough,” she said.

“Right after, I texted my mom and just said, ‘I’m sorry,” she added.

Demi insisted that not spliting with Joe Jonas caused her problems “I wouldn’t credit my meltdown to a guy. There was so much other stuff in my life.”

About childhood complexes: “Those girls never gave me an explanation for why they were bullying me,” she said.

“One of the words they called me was fat. At that age, you think, ‘Oh so I don’t have friends because I’m fat.'”

Demi checked into rehab for “emotional and physical issues”, also she revealed she suffered from bipolar disorder and admits cutting herself since age 11.

[Photos: Elle]