My aunt told me something quite interesting at our daughter's birthday.
Her mother (my mother's stepmother) told her that my mother had used with a donor's sperm conceive because my father was infertile. Now, my aunt says her mother was not the most trustworthy person in the world, but there's still a possibility that my mother's husband is not my biological father.
There are details that would corroborate this. I was conceived during their holidays, when they were both almost 40. My mother told me about my father's fertility issues once - low count (that doesn't suddenly get better with age, does it?). They named me after her aunt that allegedly helped with the procedure.
It would explain some other stuff as well. Like how come he resented me so much and wanted to appropriate me so badly at the same time. And how she would feel guilty and thankful about him accepting another man's offspring enough not to make waves about his fathering.
I have no way of knowing except taking his DNA sample without him knowing. I can't just ask a pathological liar, can I? My husband thinks nothing good can come out of taking someone's DNA sample behind his back. I don't know.
I only know I've started having fantasies about my REAL father.