All the help I can get with this situation? IPhone 5s?

I have a friend he texts me everyday and he uses 1 phone to text me and someone else… Everyday he texts me in the morning to talk to me… He has an iPhone 5s just like me. And since yesterday morning when I woke up there was no text… So I texted me and it said "delivered" so that means his phone is on.
But I didn't get a reply all day and I kept texting him… And they all said delivered but none of them said "read" and usually if his phone is off, it wouldn't go as a iMessage, it would go as a text message… But today and yesterday i don't know what's been going on. I know his phone is on… So please tell me what that could be? Could it be he forgot to pay his bill or something? And TRUST me I know there might be something wrong with the phone because we always have good convos and we were having a important talk that he said he would continue with me on Wednesday… But please would could that situation be

He could be busy.

Was it imessage?

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