I texted my ex-boyfriend a few days ago and didn't return until noon today. I just replied, and he didn't reply to me again. What does he mean?

After all, he is an ex-boyfriend He should have his reasons.

You sent a text message for several days before he replied to you. If you don't take the initiative, you either don't value you or you are worried. After all, it is a former lover relationship, and he also has absolute freedom to do anything personal. It's normal that he doesn't want to reply to you and keeps his distance from you. You don't have to pay too much attention to these.