My ex-boyfriend treats me like crap - why is that?

Me and my boyfriend were together for 8 months, but then broke up because he said he did not want a relationship at the moment. A month later he came begging for me to take him back and saying he loved me more than anyone. I did. Two weeks we spent together that were perfect, he treated me like princess, but then his friend called me his friend - and I realized we were just "seeing each other" in his eyes as he still did not want a relationship, but just wanted to see how we can do together first before committing (we used to fight a lot before we broke up, so he wanted to see if we can go without fighting for a while). I wanted a serious relationship and after finding out he had sex with a girl after we broke up (he said he needs rebound and never spoke to her again), we ended it. We haven't spoken for three days and I went to the concert that we were supposed to go together with my guy friend. He texted my friend asking if I was still going, and after learning that I was going with my guy friend - as friends - messaged me saying he is coming and coming not alone, and asked not to make a scene. He walked with her past me and my friend at the bar on purpose and I ignored both of them. Since then we haven't spoken again, until today (3 days later), he asked to return his things whenever I am available. I said he can come pick it up - but he never messaged back or came. Why is he treating me like crap and hurting like that? Showing up with a girl in front of me, then just ignoring when needs his stuff? Any advice? I really love him and wanted future with him.
My ex-boyfriend treats me like crap - why is that?
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