I am so sorry you didn't find out about your health issues and that they could be overcome before you parted with your little cat. I can only imagine how painful that decision must have been and how awful it was to find out later that it had been unnecessary. I hope you are able to believe that she is now cared for and settled in her new home and that one day you will be able to give your heart to the next cat that finds you. I think the idea of volunteering and meeting cats through that route sounds like a positive way both to meet and see if any of these little balls of fur steel your heart, and also check that your allergies can be managed before adopting so you do not have to go through the same heartbreak again. I hope that your health does not mean something like the volunteering would not be possible for you. I will be thinking of you and hoping that you continue to heal this pain, and that you find another cat to give love and care to.