I have a four-year-old female cat. She had a male companion until she was 6 months old, when she lost him to an accident. Ever since, she has been alone. My fiancée and myself have a very busy life. I only spend 2-3 hours a day at home in the weekdays. My fiancée, although she works from home, she travels quite often. The cat ends up spending the whole day on her own.
My only concern is my cat's well being. I wonder, if there is any scientifically-backed reasons to adopt another kitten, to be a companion for my cat. Does my cat feel lonely, sad, or depressed because she does not have anyone to play or fight with? Will another cat contribute positively to her well being. Is there any research on the topic?