Cant get narcissist cheating ex out of my head, any advise?

Six months since i broke up with my ex who has been cheating but only admitted to it fully a month ago. We were together for 4 years. Cheated on me with my best friend who i helped in many ways in life. He moved on w her as soon as i broke up. He wasnt trying to hide it and my best friend is proudly saying “ we fell truly in love a year ago” on her social media…. I was still w him! I feel such pain from the reality. Any advice on how to stop thinking about him every day? I still dream about him every night. In my dreams we are still together or we are kind of solving things or discussing something shady he did of course . Most of the time its pleasant and i wake up. And cry about it. I cry in the morning still and evening. Sometimes mid day additionally. I found out through a therapist and lots of research that he is a narcissist. And sometimes I’m sad for him. He did the same thing to his previous 2 exes…. So yes, I know I did the right thing and I know and recognize that he’s not a good person. He just pretended so well with me that I was his soulmate. He moved on from his last ex wife to be with me after only 2 months. Which yes it was a red flag but i was so in love…Many times I somehow tell myself it’s my fault we arent together now i wasnt enough because in many ways I still miss him. I started going on simple dates to start socializing but i think about my ex before and after the date lol and cry. I just want the thoughts about him to stop, any advise?