Why would my ex pretend he didn't see me?

Today, I was the only one walking down the stairs as my ex was sitting at the table at the bottom. When I was about halfway down the stairs, I noticed him glued to his phone, and he kept pushing back his hair. I’m sure he saw me, but I am wondering why he was acting like he didn’t. Sometimes, we do still talk when we see each other at parties, and he always claims he misses me or loves me. But I try not to take it to heart because we are usually drunk when he says that. But after our encounter today do you think he actually still likes me or was nervous to see me?
Why would my ex pretend he didn't see me?
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