Thanks guys, it was pretty upsetting as she was a relatively young cat, no more than 6. They came to me as a pair 4 years ago from a rescue centre, TC is much older, we reckon around 12. Apparently he's always lived with a friend, before Slinky he had another partner in crime. They did chase each other round the house but I'd always come home to find them curled up together. When I get home he's always waiting by the back door to go into the garden which he never used to do and I think he's looking for her. I didn't bring her home from the vets and did wonder afterwards if I should have done so.
Any ideas on how long I should leave it before I look for another companion for him - sooner rather than later?