He's nitpicking, Karen. My H does it nearly every single time he comes by. For no reason whatsoever, he'll walk around every room in the house and find something, anything, wrong and be sure to point it out to me. The kids left toothpaste in the bathroom sink, they didn't put a new roll of toilet paper on the holder, clean folded clothes I place on my bed that I haven't put away yet, or leftovers in the fridge. It irritates the crap out of me, and I feel like saying, "WTH do you care? You don't live here anymore." I certainly don't complain about what his place looks like nor do I have the desire to.
I think it's just their way of convincing themselves that this environment is all wrong for them, making the decision to leave that much easier. They refuse to see what's good in the home.
Don't let H get under your skin. Tell him you're sorry the mess bothers him and leave it at that. Change the subject to something more pleasant or walk away.
Getting over a painful experience is much like crossing monkey bars. You have to let go at some point in order to move forward. ~ Joseph Campbell