It maybe that you son is undergoing what is called a homosexual panic which is extremely anxiety provoking. From what you describe he is very upset and depressed to the point of suicidal ideation. I would therefore make an immediate appointment with a psychiatrist, community mental health center, or Department of Psychiatry of a University Hospital for evaluation. In the meantime be supportive and optimistic that things will get better as they probably will, If things should deteriorate and he has intensified thoughts of suicide or a plan then do not wait, but call emergency services so he can be evaluated for hospitalization and stabilization on medication. Best wishes and good luck.
I believe he is have an acute anxiety reaction and although he may require psychotherapy and medication the likelihood is he will return to his former state. The exception to this if there is some serious underlying emotional disorder and there is no way of knowing this without an in depth interview. But do not jump ahead. Allow the interview to take place. I am being candid about the possibility of something more serious so that you have the total picture of possibilities not because that is what I think it is. I assume the doctor he is seeing is a psychiatrist. A family practitioner is not a specialist in this field and will probably refer him to a psychiatrist and I am looking to save the extra expense and time involved.
Again it is very difficult to make a diagnostic impression without an in depth interview, but I understand since he is obsessing you might think it was OCD. I am of the opinion it is not as there are other symptoms that are needed to justify an OCD diagnosis. Like I said take it one step at a time and try for him and you not to over react. It is less than 24 hours before you get a professional opinion.