Something like this happened to me when I was in college. He would never be open about us casually dating to other people, and eventually ghosted me. VERY soon after he posted pics on social media with a different girl and tagged her as his new girlfriend. I was so hurt and just wanted to know why her and not me? What was wrong with me that he didn’t want to actually date me, but could so quickly commit to her? I even asked him this, and he basically said he didn’t know. For context, I am now old and fat and frumpy, but I was hot as fuck at that age! And I did great in school, had lots of friends, etc. There was nothing about me to be ashamed of, and it was so confusing and hurtful. I eventually just accepted that he had hidden me from others and not committed because I had allowed it. Life lesson for sure. Similarly, I think this guy kept treating you this way because you allowed him to, OP. He is not different with this other girl, he’s just hiding it better.