/feels/ - Advice & Venting

How do i stop thinking about him, its been like 3 months now and the last thing he told me was to leave him alone. When he was distant and pulling away i kept getting closer and closer and it probably pushed him off and annoyed him. He said that he mentally checked out a long time ago and when he called me on the phone that we are over it felt like my whole world is going down, i was legit getting panic attacks at night and i lost my appetite and im too afraid to text him since i dont want to know if he blocked me. I just want him back. We were together for 8 months and around the 1-3 months it was good and it kind of drizzled down around 4-5 month were he has this hot and cold behaviour. For example 1-2 days he is warm and approaching and next 1-2 days he is cold and distant and this attitude alternates. Everytime he pulls away and acts cold and distant i kept asking him whats wrong and he kept responding that hes alright, hes okay and nothing is bothering him. Like how would i know there is an underlying issue if he conceals the problem by refusing to talk to me. Just the idea of him being with another girl and being intimate and having sex kills me in the inside. I just work it out and fix it. I need help. This hurts so much.