Pile on more guilt

I have been a working Mother since September of 2003. I am very lucky to have my Mom take care of the kids while I am at work. As most of you already know, I still have TONS of guilt about being a working Mom. There are days when I feel less guilty than others, but over all I feel like crap. Well, just the other night, my darling 4 year old son says the following during dinner:
"Mommy, I want you to be home all the time and not work."
UGH! My verbal response was something like "Mommy has to work so we can have nice things and do fun things, blah, blah, blah." Inside I was DYING! I was screaming "Mommy does not WANT to work. Mommy WANTS to be home taking care of you and Ava - doing all the FUN things that she misses out on." I knew that I could not tell him this, however sometimes I wish I could. Just so he knows that I'd rather be with him and Ava than at work. Hopefully, deep down he already knows. This September when he starts kindergarten - gasp - he'll probably miss me less. However, I'll still feel like crap.