Texting

I've been casually flirting and texting with a guy. Usually he texts right back or within a few hours...on Friday I texted him and he didn't text back which isn't like him. A different time before that I texted and he didn't get back to me for a few hours, but still did. Our relationship with texting is very sexual and clearly that is all either of us are looking for. (No judgment please). Could it be that he's losing interest or am I over thinking the situation?