Why Do you get upset when I don't reply to your messages?

I was texting my boyfriend and he was not able to reply to me right away. I went in to a bit of paranoia which is not good and I was not able to control myself at that moment. I was texting him at around 5:00 PM and he was able to reply at around 9 P.M. He did explain why and I was OK i was not really mad or anything just wanted to know where he was and why he was not able to reply right away. Then he asked me this question:

"Why Do you get upset when I don't reply to your messages?"

I replied to him:

"Texting me that you are busy or your doing something important, or you're on your way home is making me feel that you are here beside me even if we are apart from each other. You know that I love you and I constantly think about you especially when I'm not doing anything. :)"

I always text and update my boyfriend even he doesn't ask me because I want to give him that feeling the feeling of importance than in everything I do even if it's small I make him feel that he is a part of what I do. My might not know the significance of that but I'm hoping he would someday he he he