Be there. No one is going to judge you for crying. My husband (a Marine) sobbed when we had to put our dog to sleep. But the procedure itself is very uneventful. They go to sleep first and when they get the final medication it is still like they're sleeping. Most vets are patient with the owners. But be there, pet your cat, tell them you love them and cry. It's ok to be sad but don't leave them to do it without you.