Last I heard, a person has the right to work or not, as s/he wishes. (Of course s/he runs the risk that the work will disappear.)

You have the right to acquire and dismiss therapists as you wish. I believe a therapist has a corresponding right to accept or decline patients.

Unless you have been involuntarily committed, you have the right to leave therapy.

Question (b) is not quite coherent.

Bottom line:
There are many more therapists than would-be patients. Unless you are extremely wealthy, you’d be wise to be grateful for what you’re getting.