If you're obsessed with someone, you need the professional help, not an impossible person.

I can't talk about this in such detail on domestic websites because I might be recognized. My mother tongue isn't English. This event may be very unusual so there'll be many details involved. When I was 16 (now 25), during the summer break when graduating from middle school, a stranger, who was an online friend of my school classmate, pretending to be her after somehow getting her social media account passwords, and managed to get my phone number and photo. Because I thought it was really her and we're all so familiar, I casually took a picture with the front camera of my phone. I have a very recognizable face but haven't any overly conspicuous features like moles or buck teeth, the photo didn't look like the real me because of the lens distortion and without any post-processing, but people who know my real face can tell it's me at a glance. While pretending to be my classmate, he also posted a photo claiming to be himself (he used her identity and said "it's my online friend"), and claimed to be 23. Everything seemed normal afterwards, until he went offline, after a while my classmate went online and asked me what happened before. I sent her the chat log, she said it wasn't her who spoke to me earlier. I was confused and asked her what was going on, and she said she didn't know either. After a while, my classmate told me that he tried to convince her to let me add him as friend (I set the privacy verification question) and sent me a screenshot of the chat log. I asked why does he want to add me and told her to tell him. Later she replied "He said if you don't agree he'll do something" (sic). I asked her what he'll do exactly, she didn't say. I'm confused so added the man. I saw his profile, it's complete, also said that he was 23 and had the photo he sent me before. Then he wooed me with offensive words and I calmly said no to him, it's not only because he's not my type in terms of the photo but also the way he's doing it's unacceptable. He immediately threatened me with self-cutting. He also attempted to pressured me for nudes. I tried to persuade him for more than an hour, during this time, as long as I showing refused, he threatened me again and showed desperate. I was want to pretend I had a boyfriend or I was a lesbian, but I was afraid he would find out or already know my real situation in some way and be more dangerous to everyone. He didn't threaten to hurt me or my loved ones and said he would be nice to me. I was shocked to dissociation and "fighting for my sanity". I know it's not my fault, but it only make me not feeling guilty. Finally I found that he was really unable to communicate, I had no choice but to delete him and had to delete my classmates. We're just school classmate and haven't mutual acquaintance, my mental state didn't allow me to deliberation and/or tell her what happened. Then he called me several times a day at certain times, I put my phone in whitelist mode. It lasted half a summer break (about a month). The age of consent in my country is 14 (at least at the time), but what he did involved coercion, it's still a crime and subject to psychological counseling (it was 2010s, the difference between the appearance of 15-16 yrs and adults is generally only a slightly childish face and clothing style). I know this but I can't seek help because of avoidance symptoms and memory loss. Since my only two symptoms were loss of relevant memory and avoidance, no one noticed. Memory loss isn't the same as total forgetting, it can still feel wrong. After more than 2 years I started to naturally and slowly recover my memory, I don't know how many years before I fully recovered memory and recovered from the avoidance symptoms. I'm afraid of romantic relationship now, because I'm afraid of meeting such a person. I'm also instinctively afraid to answer strange calls unless there's a mark such as "Express", even though I know I've changed my number for an unrelated reason when I was in college. I didn't cancel the whitelist mode until I changed my number. I speculated that he probably have discovered me through my likes and comments on my classmate. I'm always tough, but still almost broke by the situation. If I'm a Transformer, I'm not afraid of someone threatening to hurt me; but if someone threaten to hurt themselves, it's useless that even I'm made of dark matter. If this event got any worse and broke me completely, I may think that those vulnerable people are social harmful and need to be eliminated. If someone is doing this because of mental illness and/or personality disorder, what they need is professional help, not an impossible person.