Why is my ex so hostile towards me?

My ex and I work together, I see him almost everyday. he broke up with me because he will be moving to another state in a few months and “didn’t want to hurt me or fall in love with me” before he left. He wanted to be friends with me, but I told him it was going to be hard. That upset him, and during work, he could barely make eye contact with me. This bothered me because it made me feel very uncomfortable while working. I approached him about it and he said it’s hard for him to look at me because he feels guilty for what he’s done to me. Fast forward a couple of weeks, barely any contact between us (only work purposes), and I was feeling better. I found out from someone that he had a new “girlfriend” and was posting about her on his Instagram story. I never saw the posts, he blocked me from viewing his story. This made me very upset, so I unfollowed him on Instagram, on Facebook. I stopped all contact with him, and if I needed something from him at work, I would talk to his boss (we work construction). He tried to start talking to me again before New Years, offered me chocolate and lunch and requested me on Instagram. When we returned back to work, he approached me, told me he missed me, has feelings still, and complemented me on my weight loss. He told me he never considered that girl to be his girlfriend, because a girlfriend is someone who you share feelings with. He considered me to have been his girlfriend. He told me how beautiful I am. I’ve lost 20lbs since and am more confident. We share work friends, and he’s made really rude comments to them. Now, he won’t even look at me. It’s almost as if he’s so angry with me. He ended things, not me. I know he’s been asking our friends if they relay messages to me, because after I found out what he said, I decided to no longer entertain him at all (avoiding him, asking his boss work questions, deleted his IG request). I’m trying to move forward, but now that he looks at me like I am the worst person alive. Any advice?
Why is my ex so hostile towards me?
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