If you think horrible thoughts you're going to create a horrible situation.
It's very simple, get rid of the key chain. Go throw it in a river, a pond or lake.
Then go to the mall and buy your husband a nice new keychain and have it engraved and present it as a gift from you. Maybe you should get matching engraved key chains.
Don't think about the other keychain ever again.
If you keep thinking about the other key chain you are going to bring horrible feeling right back.
It's time for you to learn to get your hysterical gauge under control. You can only control your atmosphere if you can control your emotions.
You have to choose not to be upset about things.
Do what you are supposed to do...then forget about it.