If your employer believes that your stress is work related, it will be difficult for them to allow you to return to work if they have reason to believe you are not fully fit.
They have to protect you from further stress, and be sure you will not be claiming for compensation. It is a real worry for bosses these days.
Also, your employer has a duty of care to all the employees. If your illness is such that your colleagues could be affected then he is doing the right thing.