The Space Between..."pre k" and Pre-K

Yesterday was the first day of school. Luke's first day of PreK.
I'm totally fine. I didn't get weepy, I wasn't preoccupied with worry until I knew he was "home".
People kept asking me all day - how was I, did I cry. I've seen other mothers still teary eyed over an hour after drop off time. I was excited and marking in my heart the first of many "first days of school". But not super emotional...odd in hindsight because I do consider myself an emotional person. So I got thinking.
Think, think, think...as Winnie the Pooh would say. And here's what I keep coming back to -
I have pretty much always been a mother who works outside the home. (I hate the term working mother.)
I was working retail part time from the time Luke was about 6 months old until just before I found out I was pregnant with Megan. I was home for my whole pregnancy with Megan, but got a part time job when she was 2 and a half months old - and I've been there ever since - but now full time. And not even that - my job is 45 minutes away. I leave before 8am and am never home before 6pm. Back to emotional separations though.
I guess what I'm saying is that I'm used to leaving my kids places. Not only that - my kids are used to be shuffled around and every morning they ask, "where are we going?" or "who will we see today?"
Pre - pre K, I felt minimally guilty. This week - with about 16 years of first days of school ahead of me (not to mention - sports, concerts, conferences, open houses, sick days, school vacations, etc.) the space between home and work seems to large, to full of things that shouldn't be as important as my kids. This week (and probably from now on)- I want that space diminished.