Dealing with my ex-stalker

Hey everyone! I need some help and I’m not sure if this is the right group but here I am.

SO SORRY for how long this is. If anyone has a similar experience I would love to hear/share.

Im 18, and one of my slightly older ex-coworkers used to harass me constantly online. It started in September and continued on-and-off until my new-ish boyfriend messaged him in March. When I say harass, I mean that he was constantly (all day, every day for week-long periods with breaks in between) sending me messages over Facebook telling me about how much he loved me and how important I was to him. Usually 30-40 a day. He would send me messages about how lonely he was and how horrible I would make him feel, and ask for pictures of me smiling. He used to go back into old messages (before I stopped replying to him) and change his reactions to them to sad and he would talk about my profile photo and other stuff on my account. It wasn’t great. I felt way too horrible and guilty to block him because he made it abundantly clear that he was alone in the world and I thought « hey, if he tries to hurt himself at least SOMEONE will be aware of it and will be able to help ». At some point, he stopped showing up for his shifts. I stopped replying because it intensified it every time. I can’t stress how much it was. Eventually he switched over to my Instagram. I never opened any of the messages, on Facebook I read them through notifications and on Instagram I hadn’t accepted his request so it never sent read receipts. We didn’t know each other at all while working together (maybe a 3 month period?) and I would ask him questions like « where is this spice? » but literally nothing else. It was a random coworker. WE DID NOT KNOW EACH OTHER OR TALK TO EACH OTHER, EVER. He would wait outside work to see if I’d go out. He turned up on my street several times. He cried to me and followed me for four hours because I wasn’t sure how to make him leave and didn’t want him in my home. He described to me how my voice changed when I spoke French (bilingual city), how I walked, and other tiny details about me that made me so deeply uncomfortable. We didn’t even talk!! We weren’t coworker-friends, he was barely an acquaintance. I can’t exaggerate how little we knew each other. Anyway.

My boyfriend sent him a message I’d written with hotline numbers and well wishes the most recent time it started up again (he was talking about doing drugs to forget me and getting sick, not eating, accusing me of hurting him etc). He (ex coworker) sent a couple messages back but we never answered and thats the last of it.

My issue is now this: I can’t get him out of my mind. The fears that I had when I walked alone at night were completely replaced by the image of him (now he’s the anonymous man grabbing me and tossing me into a car or watching me through the windows). I’m always nervous that he can see me and is waiting for me. Whenever an account I don’t recognize interacts with me online my heart jumps and I get so nervous. I see him in crowds, when I can’t see boys’ faces, everywhere. I’m scared that A) he’ll start up the messages again because he’s gone on “breaks” like this before or B) he’ll turn up dead and it will be my fault because I’ve cut off the only line of communication he had (I blocked him after my boyfriend sent the message because I was scared he was on my instagram). Even posting here I’m nervous he’ll somehow see it, recognize me, and start this whole thing up again. I’m scared.

Part of this post was definitely to vent but... has anyone else experienced something similar? With a stranger? What can I do to calm this anxiety? Again, sorry this post is so long. Thank you all very much.