There are lots of reasons.
Could be sleeping or in the shower. Maybe he forgot his phone some where or has it on set to silent. Maybe he's in a place where he can't get reception or decent signal. Maybe his phone fell in a toilet or got ran over by a bus, that last one happened to my ex not too long ago. So many reason.
Being busy
Perhaps their wife is in the room.
Maybe he is trying to avoid having to do something he doesn't want to do. If he responds, he can't say he was unaware of the text messages or phone calls.
Busy, phone is dead, asleep, in a dead zone, feeling like he might need space because his needy girlfriend won't stop texting.
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