I think it’s one thing not to reply to a text if maybe you lived together or at least saw each other each day. But if you’re doing neither of those things, I don’t think it’s unreasonable to expect a romantic partner to text back the same day you sent them one. He may just be a good guy with poor communication skills. Maybe he had a bad relationship were his partner was texting him constantly as a form of controlling behaviour. It could be any number of things. My advice would be to talk to him about it. Be open and tell him about your past experience and how his lack of communication makes you feel. Hopefully that can help you both reach a common ground