Demi and Joe did date. They met on set at the Disney movie "Camp Rock" back iin 2007. It was a mutual attraction. They did indeed date. They really didn't start their dating officially until 2010. But, it only lasted a month. According to Joe, he soon saw she was struggling with drugs. He stuck around as long as he could to help her out but he was miserable.
He simply could not fix her although he wanted to and he did try. So, he broke up. Now, he is engaged but she...is not. She still has some very real struggles in her life and hopefully will tend to those before worrying with a relationship.