Why would my ex still look out for me when his woman is better looking than me after her cosmetic surgery?

This is a love that started when I was a kid. He’s ten years older than me and I had a crush on him since I was 13 now I’m 29.
He has a beautiful woman and 2 teens with her. She’s older than me but looks young and beautiful especially after her cosmetic surgery her body looks amazing. The only flaw that she has is taking him from her best friend years ago. It was his decision but still they both cheated on her and formed a family out of the pain of someone else. Anyways, we kinda dated years ago when his wife and him separated for a while and he wanted to marry me but I couldn’t keep up with that in my head. He almost confessed everything he did and I knew that he would do the same to me. I suffered for years and now I feel nothing. I might still feel attracted but I like him more as a friend. Somehow those deep feelings became very tiny. We’re neighbors for years so that’s why I know and everything is clear between us. Sometimes they break up again because they’re both cheating especially him but she just doing it for revenge I guess.

He treats me like a friend, an obsession, he remembers every single detail about me, stalks me on social media and I think of more of an obsession but not love.
Why would my ex still look out for me when his woman is better looking than me after her cosmetic surgery?
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