> i have a patient 40 yr old who is intellegent and hardworking, hes is seemingly sober and composed but he thinks he is madly in love with a girl since a long time. hes constanly hounds and harasses the girl. any form of psychotherapy is fruitless with him. please advice regarding diagnosis and management

I would suggest referring him on for a psychiatric assessment.

Does he know that the person he is following around is not in love with him, or does he believe that she is?

Sometimes people have delusions where they believe a person is in love with them even though the person is not.

I would be a little concerned that the person he is following might press charges against him if he is following her around and harrassing her.

Therapy would probably be the way to go... But a dx assessment by a psychiatrist would probably be a good first port of call and he may benefit from medication.

It is hard to say without knowing more... Could be obsessive thoughts about her (OCD) could be control issues... Who knows...