Why does he view my messages and not respond?

So long short... I had a friend who was in prison. I talked to him for 2 years. He gets out I don't hear from him. I get he has a life to caught up. But I don't think a simple high in the passed 2 years he's been out now is a lot to ask. So I recently sent him a message on fb. He responds over a week later. I messaged him saying hey been a min hope all is well with ya. But why did you ghost me? He says sorry and tried to video call while I was sleeping. So I message him again saying all is forgiven but why did you disappear? He said he was tired of feeling like he was hurting me. So I asked why he thought that. He views my message but didn't respond. It's the next day and curious about why that is.

Why does he view my messages and not respond?
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