I am sorry for your sadness. There have been so many beautiful responses to you so far, I hope that they have brought you some peace.
My mother is 86. When she was 5, her father died. She led a very tumultuous life with her mother and younger sister and step-father after that. Very poor. Moving around all the time. No stability. She has always borne the loss of her father as the great burden in her life. What might their lives have been like had he not died so young. I think it really has haunted her and weighed upon her. Yet her life, now, is so long. She has been an adult for 65 years! She has had success and happiness, yet she still mourns this loss, this void in her life. I cannot relate to it, but I try very hard to be tolerant and respectful of her feelings.
So I sense that you, too, will always question this and know that you really may never have any answers. That is hard to accept, I'm sure.
We are all made up of so many different kinds of families. The traditional family -- mother, father, child -- does not exist that much. Perhaps never did. But family can be strong; however it is characterized. I bet you have experienced and work hard to create strong family. It sounds like it, anyway, in your words. I'm sorry that your biological father was not able to find a place in your family. If you work to keep your family strong, then, you will honor him, because whether he intended to or not, he helped bring you into this world. That has to mean something, whether it is clear to you or not.
Best wishes. Hope your family here has helped you feel better.
Marguerite