I have a problem concerning my boyfriend's behaviour. When i met him he had an obsession that he had cancer. he had cloded his bussiness and waited to die in a room. I helped him overpass this obsession by taking him to the hospital for medical examinations and he was persuaded that he was alright. He started up his bussiness again and was very happy for a while. But about six months ago he started being suspicious on me saying that my friends are immoral and want to influence me and that my parents don't really like him. So he is trying to isolate me from them bit by bit. Do you think he is suffering from a mental disorder or is it just a character problem?
Do not let him isolate you from your friends or parents.
You ask "Do you think he is suffering from a mental disorder or is it just a character problem"? By this you seem to indicate that character problems are less worse than mental disorders. This need not be so. Character problems are by psychologist called "personality disorders" and they are, unfortunately, difficult to cure.
SSRI medicines might be able to cure the obessive elements of your husband's behaviour, but they may have side effects which he finds unaccepable. Psychotherapy might also help, and does not have problematic side effects.