he hasn't texted me back

What do you do when you know your SO isnt busy and he hasn't texted you back for the whole day?
I've talked to him about this many times about how i'd appreciate if he gave me a quick text updating me like in the afternoon and night time because i dont like it when he takes many hours to reply  back and he has agreed.
But some days, like today, he hasn't texted me back at all and i cant help it but end up feeling worried and sad :(
How should I go about this?