My boys are only 7 and 9... and they were saying the similar stuff to me... we spend more time with Grandma/Granddad/Daddy... than with you because you are always working. For the last couple of weeks, I have made a conscious effort to be home and spend time with them in their world.... think you and your son could just go out for a dinner or on a drive together?
I don't think once a week is so bad... I mean... you need the support right now too...... and he doesn't understand that.... probably cause moms are bad a$$ people... and don't need it!!! *wink!
Kids are hard to read... because they don't know how to put it properly into words how they are feeling....... (((hugs))) .... what do you have planned for the holidays with them?