Why can't i let him go? my confusing breakup story

Me and my ex dated from October 2023-August 2024 and then we were in a weird limbo until December of 2024 until he finally blocked me on everything. We haven’t spoke at all until March of this year. I reached out because I realized I had something important of his and from there it spiraled into us basically being back together without the label. Within that first month of talking again he was talking about our future together (marriage, kids, moving away, etc) and I really thought it would be different this time around but shortly after that month mark hit, he became so cold and hateful. During our first big fight I found out he was in a relationship pretty much the whole time we’ve been broken up and that crushed me because that whole time all I could think about was him. I’ve always been the one to hold on no matter how bad things get but he just wants to run away from any accountability or issues. It’s been hell these past couple months to say the least, I don’t know how to let him go even when he says the most awful things to me. Just this Sunday we hung out after a really good Saturday night together. I asked him about my birthday plans since we were planning on spending it together and he basically dismissed it which led me to crying and being upset. He then told me that he’ll never wanna be with me and we don’t have a connection but we can be friends. I’m just so confused and hurt but I can’t seem to let him go no matter how badly he hurts me. It’s like I don’t believe him but I do at the same time. I just can’t understand how someone can switch up from day to day, one day he’s calling me baby and we’re intimate but then the next it’s like he hates my guts. It’s like he’s a completely different person but I keep holding onto the version of him that I fell in love with. I feel pathetic and dumb that I can’t just move on like he clearly wants me to do. I’m gonna try my absolute best to go no contact for as long as I can after I give him his stuff back in the morning. I hope I can just let it go but in my head I feel like after so long I’m gonna say “well that was long enough maybe he changed his mind” and want to reach out again. I feel like I’m burdening my friends with how much I talk about him so I’m hoping this app can help me when I just need to vent and let it all out.