My Son Is 22 Yrs Old .he Is Studying In

My son is 22 yrs old .he is studying in a university and that's why he has to stay alone somehow he has imagine himself to have a girl friend who belongs to royal family and all the time he tries to convince other that she is real.now he lost all his interest in studies.i m worried.he went to a psychologist but his situation is getting more complicated .what can I do