Same here, we have been told two years before it is safe to have another cat in the house. The virus which causes Feline Leukemia is nasty and can stay dormant for over a year
My cat had FISS (feline injection site sarcoma) which is a rare but aggressive cancer. With surgery and chemo, he lived an additional year but only a month after the conclusion of his chemotherapy treatments, the cancer returned. At that point, we opted for pain management until he reached the point where we had to make the difficult decision.