The American Psychiatric Association (APA) defines diagnosable mental disorders as:
health conditions involving
- Significant changes in thinking, emotion and/or behavior
- Distress and/or problems functioning in social, work or family activities
It sounds to me like you have found an antidote to being lonely. At 58 and single, you have lots of practice with a fantasy life that is harmless. It doesn’t negatively impact your work life or your ability to make personal relationships. It isn’t distressing to you. It’s a private activity that you enjoy.
I don’t see any reason to change what you do unless it starts getting in the way of functioning or you start feeling regularly upset by it. If that happens, then see a counselor to talk about whether you should be concerned and, if so, what to do about it.
I wish you well.