the state of being obsessed with someone or something.
an idea or thought that continually preoccupies or intrudes on a person's mind.
Being obsessed is a mental illness. When someone becomes obsessed with you, it is unhealthy and potentially dangerous, especially if the obsessed party is mentally unhinged.
Symptoms: Escalating fixation, often to dangerous levels that include stalking of not only the target of the mental idiot's fascination, but also family and friends, hanging on every word written on a website, believing that every word written on a website is somehow directed at the obsessed person. Paranoia, schizophrenia, substance abuse - all should be taken into account if you care for the person you think may be losing his shit.
If you know anyone suffering from such delusions I encourage you to forward this number to them: 1-800-662-HELP (4357)