You first remind yourself that you do not control the actions of your cat when you are not home. Cats are shelf jumpers. The higher they can get, the happier they are.If you have the money, buy a climbing pole with a very high shelf, and the cat will be less likely to try and jump on your shelf. Hopefully. You can get climbing poles that go all the way to your ceiling. This is what I used to keep mine from climbing the drapes.

Second, you did not do this on purpose, nor was it meant to be a mean thing to your fiance.You were actually honoring him, by making space and putting his things out.

Even a good thing can sometimes turn out bad, but it's not your fault. And when your fiance gets home, he may get upset because his things were broken. That's a natural response to something lost. Just remind him to yell at the cat, not you. You did nothing wrong.