Have you told him how you feel? Have you figured out when is the best time to text him so he isn't "busy" and can answer quicker? I remember when I was a kid and my mother would ask me to do some chore when I was busy and then get mad because I wouldn't do it right away; when another is doing something of their own, I think it's kind of rude to expect them to respond to us, like we are more important than their own lives/stuff.