Reaching out to half sister that does not know I exist

I am new here. I was given up for adoption as a newborn by my teenage mother who had an affair with a 30 something married man. I have always known I was adopted. At the age of 24, I sought out to find my biological mother. I have been fortunate enough to meet my birth mom, as well as my two half sisters, in 2006. We have been in contact on and off through the years through social media and family events. They have become my family. I did reach out to my birth father, after I was given his name by my birth mom, in 2006. He reluctantly agreed to speak to me after I emailed him. He stated I was a product of a one night stand, he had a daughter 3 years older than me who did not know I exist and wanted to keep it that way. He said they were very close and how proud he was of her. He said he did not want to sign my birth certificate because he did not want to be a father. He backed out of meeting me the few times we were supposed to, and made it clear he did not want to get to know me. . I did not reach out the half sister because I hoped he would come around and want to get to know me and my family. Over the years, I have accepted this is not the case. After watching my own daughters grow and trying to explain the dynamics of my family (my family and birth family) the desire to reach out to the half sister has grown. I know she is married with a son of her own. I am torn because for 39 years of her life, she thought she was an only child. I would shatter what she knew and thought. Would that make me selfish? Then I think if I had a "secret sibling", I would want to know but that could be my skewed perception being an adoptee. I feel like it is a piece missing from the puzzle that I would like resolution. I do not know owe anything to my birth father nor did I make a promise. I am at a point where I could handle any reaction, even if it meant no response or not wanting any further contact. What do you suggest or think?