Ex boyfriend being mean and we work together?

Me and my ex had a bad breakup a few weeks ago. Like 2 weeks. Unfortunately I work with him and long story short he's just been very childish. There was a delivery that should have gotten picked up but wasn't and nobody knew why because he failed to tell me the issue so everybody was asking me what happened etc. So I had to call the company and that's when they informed me of what happened (not gonna bore u with explanation lol). Then today I see him (he's at work early like 2 hours ) and since I passed him up right when he came out restroom, i naturally said"Hi Luis!" And he jus looked at me and wanted to ignore me but then was like "what's up" all mean. Now this situation just sucks cuz we work together. I refuse to bring personal be in workplace so not sure why he is making work difficult Why do guys act this way please? Just natural asshole? Any advice how too stick out this negative behavior? He's trying to move on but in a unhealthy way because the way he's doing it is interfering with work. I'm cordial,
Ex boyfriend being mean and we work together?
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