Why would a guy I work with suddenly try to avoid eye contact with me?

Why would a guy I work with suddenly try to avoid eye contact with me, he’s done it once before when we were passing each other in the hallway, which I guess we were doing again today when he avoided eye contact, he was on call so only in for probably like 30 minutes, and then when we passed by each other again we almost ran into each other and that time I stayed looking at the ground because I don’t wanna try to force eye contact but we hold really good conversations and usually pretty intense eye contact usually otherwise when in conversation, and every other time we pass each other in the hall he usually looks at me regularly and we make quick eye contact. I am attracted to him but I’m not sure if he’s attracted to me, I’m not even sure if he has a girlfriend or not
Why would a guy I work with suddenly try to avoid eye contact with me?
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