I am unhappy in my field of research and approached my supervisor to ask if I could transfer to a different research group at the University, which would mean getting a new supervisor. To say his reaction was bad is an understatement, he basically told me to f**k off, and said that if my prospective supervisor approached him he would give me a bad reference. I feel I have been the model student, hard working and dedicated. Can he do this? What can I do about it? Anyone else been in a similar situation?