How do you know if you have delusional feeling about someone ?

A delusion is ....: ..... A false unshakeable belief that is usually not shared by others. Can you explain what you base your feelings on to your friends and relatives who may know this person? The discussion about the nature of your "feeling" about this person with a mental health professional can help you address this delicate question.

A fixed false belief: A delusion is a very strong belief, a conviction, that is demonstrably false and flies in the face of evidence to the contrary. Delusions usually don't occur in isolation, but in the context of other emotional disorders. And here's a secret: if you have enough insight to ask, you probably don't have a delusion. People with delusions very rarely question their own conviction.