Hey Anna - I've been a lurker in this thread for a while and generally have been too appalled by Nick's behavior to want to acknowledge him, but I wanted to chime in now that you're here participating and revealing details about him. I am so, so sorry that you've become entangled with his perversions and mental problems. But I know you aren't here at all for pity and I see that you talking publicly about him is a way of taking back control, getting support and well-deserved empathy.
...but at the same time this sets off warning bells for me. This might be some latent Mama Bear syndrome on my part, but I genuinely worry that, with you acknowledging him publicly, especially since (as he implied) he can read posts here or at the very least knows you are active here now, will perpetuate and increase his obsessions with you and possibly put you in danger. Any attention or any space that he occupies in your mind is not only a victory in his minds eye, but further "proof" that his delusions will come true because you are still thinking about him. I worry that discussing him here could motivate him to take action or level-up his sick fantasies.
I am sure this has crossed your mind and I know that you know him better than anyone here, however unfortunate, so I try to trust that you know what you are doing, but I won't lie, I am concerned about what this attention from you means to him right now. I don't mean to silence you or censor you, because I love seeing there's a supportive outlet and group here for you, but I wonder if there's a way to hide stuff here from him to protect you, if those measures haven't been taken already. I saw Null's tweet to Nate earlier and was stoked to see that there's some protection in place.
Tl;dr: glad you're here, be careful, nick is a delusional fuckwit.