Um, have you considered that maybe your dad just donated sperm? You talked about what a nice guy he was. It’s possible he was so kind he wanted to help out families who had fertility issues/queer families so he donated sperm and didn’t tell your mother or you. Maybe you were conceived the old fashion way. Maybe you’ve already explored this, if so, please mention it in the article. I mean unless your mom has copped to using a donner.