It is very rude not to reply to message,SMS, at least
acknowledge. It is his fault. you might want to try message him
again. maybe he forget to reply or lost in air..
but His reply is most likely,"yup, my apologies, got something
on."
like you say, he is very shy, so you expected him to go to your
party with no friends around? who he talk too? he is sure to feel
uncomfortable .
