I am sorry you are having so much difficulty with your son and that he is struggling with his decisions. It seems like he is experiencing a great deal of anxiety, and the fact that he wants to become a recluse may be a symptom of social anxiety, but there are many other possibilities and overlapping concerns. Because of this, I would, first and foremost, I would encourage your son to go to the university counseling center. Medical colleges know how stressful and difficult the course of study can be and having your son talk about his desire to leave with them would be a very good first stop. It will also help to have him talk about the potential guilt feelings he might have about the tuition payment. The universities are typically very familiar with the needs and issues with the students and they are often in the very best position to help him.
In addition, it may be important for you and him to investigate social anxiety. While I am not trying to diagnose your son in any way, many of the things you’ve mentioned point to his need to be isolated and difficulty with social situations as a type of social anxiety.
There is some excellent information here about social anxiety that you may want to consider.
At the core of my thinking about your son understanding more about social anxiety is that you mentioned the role-playing of Doctor-patient is such a huge trigger for him. This is actually a performance issue and the specifics of that can give us a clue about the social anxiety component, Your son can make friends, but this part of his education—the performance and evaluation part is actually a specifically named component of social anxiety. If he wasn’t able to make friends this would be viewed differently, but since it is so specific it can be classified another way.
This is why I am highly recommending he speak to a counselor on campus. The avoidance of a performance-based evaluation condition can become so severe it can, indeed, cause something like what your son is experiencing.
The reason I am encouraging you to help your son see a counselor is because if it turns out it is social anxiety there are very successful treatment options. This article will outline the psychotherapy, medical, and self-help options that are available
Wishing you patience and peace,
Proof Positive Blog @ PsychCentral