Why does he sometimes read my messages & not reply?

Been online friends with this guy for years now. We have never met. We just recently started sending cute videos & messages back & forth to one another on Snapchat. We both said we have interest in actually meeting & getting to know one another. I’m confused because I feel like reading & not replying shows he’s uninterested yet days ago he was being so cute. I jump to conclusions, but I’m usually right.
Why does he sometimes read my messages & not reply?
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