Wow, that is tough. You admitted to your errors and talked with the Dean about it. You told the nurse supervising you that you were leaving so I do not see that this was abandonment. I would check with the college about the appeal process. The Dean of Nursing has someone over her that you should probably go do (Dean of students, VP of student Affairs, etc.). I would write up the conversation you had with the liaison at the clinical facility and have that person sign it if they are willing. Also I know that nursing school can be cut-throat, but I was surprised that your classmate sold you out like that. I would also see if you can drum up any faculty support for you and have them write letters of support or ,if allowed, appear at your hearing. It’s probably too late to restart the semester, but I would see if you win the appeal if you could get half off the tuition for the following semester.
Good Luck!