My ex acts like I don’t exist?

Since our breakup about a month ago we haven’t had any contact at all. When we ended things we both apologised for our mistakes and I said I wanted to be on civil terms with him. So I thought it wasn’t a bad break up. But since we go to the same university I have bumped into him twice at the gym, and both times he would literally walk right past where I’m working out and not even look at/acknowledge me. If I move to an area of the gym where he is he’ll leave and go somewhere else so he’s not near me.

Since I actually like him as a person and we have mutual friends I was planning on just smiling at him but being preoccupied but he just acts like he doesn’t know me? Why is that? It kind of hurts since I care about him/ still have feelings even though I know we wouldn’t work in a relationship so wouldn’t want him back.
Updates:
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I understand everyone’s saying to move on, and I’m doing my best to. But with all his other exes he’s remained friends/ on ok terms with them... he even follows them on social media and likes their posts. So why can’t he hand me the same respect?
My ex acts like I don’t exist?
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