A list of things that could be going on if he isn't texting back.
He’s waiting for a break in whatever he’s watching. If you’re getting a flurry of texts followed by roughly 8-12 minutes of silence, he’s either watching the game or Hulu (or live TV, for some reason). If it’s 20, it’s the opening and closing credits for a show on Netflix.
His phone is across the room charging. If his only available outlet is across the room, chances are he’s not doing wind sprints back and forth every 30 seconds to check his messages.
He’s asleep. If it’s between midnight and 7 AM this is a very reasonable assumption. But naps can happen at any time.
He’s in the shower. If it’s really important to you that he texts you while showering, buy him a waterproof phone case for his birthday. Then he’ll have no excuse.
He’s eating something really greasy and can’t get to his phone. He’s either going to finish his burger before texting you, or he’s currently desperately searching for a napkin.
He’s in the middle of a video game. AND NO HE CAN’T PAUSE IT BECAUSE HE'LL DIE AND THEN HAVE TO START ALL OVER. Once the round is over, he’ll text you back.
He’s in the middle of reps. Or maybe he’s so sweaty at the gym that his phone keeps slipping out of his hands comically, and he’s chasing it around.
He’s trying to come up with a thoughtful response. THIS IS THE MOST LIKELY REASON. HE LOVES YOU SO MUCH THAT HE WANTS TO CHOOSE EVERY WORD CAREFULLY.
He did that thing where he looked at your text and responded in his head and then got distracted. Then he went about his day thinking he responded to you and wondering why you haven’t texted back yet. See also: typing out a message but forgetting to hit “send” and having no signal and the message not going through.
He’s in the middle of a very important meeting. If anything, you better hope his phone was on silent and you didn’t accidentally get him into huge trouble.
His phone is dead and he hasn’t realized it yet. Nothing like pulling your phone out of your pocket to realize it’s been dead and you don’t even know for how long. Were lots of people trying to call you to alert you to some emergency and you had no idea? You know the feeling. But it’s entirely possible he’s going about his workday blissfully unaware his phone isn’t even on.
He’s driving and is waiting until he gets to a stoplight to respond.Don’t text and drive.