Good gravy I love this Inga. I really do like the idea of a child being comfortable enough to speak their heart - but I think it's crucial for them to make the connection that if you feel the need to say something disparaging, you need to be willing to step up and make the situation better.
As others have said, this may be a blessing in disguise. This could be an opportunity to make your house a family project rather than a "mom fixes it" project.
Remember too that the messy may feel different to your son than it does to you. Maybe the best question to ask when he says it's messy is "what can WE do to make it better?"