Son asked if I'm angry at his mom

My 11-year-old randomly asked me this last night while I was making dinner. I wasn't expecting it. I said no (which is true - I'm not angry, more just... done with her). But now I'm wondering if the way I talk about custody stuff or logistics is making him think I'm mad. I don't badmouth her to the kids but I also don't hide that co-parenting is a thing we have to actively work on. Is that okay? How do you keep kids out of the emotional stuff without lying to them?