not knowing my real father

I grew up with always in doubt who my dad was ..well, after my dad who I thought was my dad died, both my sister's reveled to me he may have not been my dad after all. My mother married three times.. my two sister's knew who their father's were, I am the only one who had been in doubt all these years and they have not helped with adding to the mystery. My older sister's dad, who I believe may have been my dad..the only reason I say this, is he always took an interest in my education and my life..and after mom passed away he told me he wished he had got to know me more through the years.. he was always thrilled to see me when I showed up with my older sister and this would frustrate my sister to the point she would get really upset at me and yell at me trying to dominate her fathers' attention..which I was never trying to do..ever, because I always thought my dad was the father of which my younger sister I shared but there was always a question..Mom said, I was three months early and Dad said, I was on time..so my mother kept a secret that was never shared.
After mom passed away he told me if I ever needed to talk he would always be there for me. He even wrote me a letter later sharing those same sentiments.
My sister's and I no longer talk.. and this morning when I woke up I had this warm feeling in my heart that he was trying to tell me back then, he was my dad. I could be wrong, but sometimes you have to go with feelings, just to get past the pain of not knowing. Thank you for allowing me to write this.