No, he's not busy. No, his phone didn't die. No, he didn't forget to text you back. No, it's not that he hasn't been on his phone. No, it's not that he doesn't have service. If you're not hearing from him, that's because he has nothing to say to you. If you're not hearing from him, that's because he isn't thinking about you.
If you're not hearing from him, that's because he doesn't miss you. No, it's not because he "sucks at texting back" and it's not because he doesn't call you back in 5 minutes like he says he would, but it's simply because he doesn't want to. No, it's not because he isn't receiving your texts and tells you "I never got it" then it clearly says "Delivered" right after you pressed send, but it's simply because he purposely ignores your messages .
If he's not talking to you but he's able to be active on social media, that should be enough to show you that he doesn't prioritize you the way you prioritize him. Stop trying to convince yourself that you'll eventually hear from him. Stop trying to make yourself believe that there's a good reason as to why he isn't talking to you.
Stop trying to force yourself to wait until he decides to make time for you. If he can't even do the little things like say good morning, ask you how your day is going, tell you about his day, and say good night to you so that you don't go to bed feeling unimportant, you need to let him go when you reach a point of desperation, when your determination is gone; what you deserve is consistency.
Same applies to the gentleman.