Why do I always feel bad if he doesn't text me back right away?

im getting very close to a guy and we text all the time, if I text him and he takes more than like ten minutes I think he's mad at me or something... but I know he's just busy... I just can't help but think he may be mad. why do I get so nervous?

i forgot to include that he likes me... a lot he's told me that about four times...