We took Smudge to the vet to find out what was wrong
What did you think was wrong?
I was afraid that it had some serious diseases like cancer or AIDS.
Hope your pet is all right. It's good that you took Smudge to the vet before it was too late.
I had it put down.
I am sorry to hear that, but you shouldn't feel guilty for your decision.  When pets have serious illnesses, sometimes the treatment can just cause them more pain.  You did the compassionate thing for Smudge.