This is a really unfortunate situation. Your biological father didn’t want to get married or have kids with your mom.
You can’t make people want what they don’t want. I hope he at least paid child support for you. For him, because he didn’t choose to be a father at that time, he probably felt betrayed and angry that your mom decided to go ahead and have you anyway. None of this has been fun for anyone.
It’s really unfortunate that people don’t discuss these kinds of issues and the possible outcomes before they have sex. But reality suggests, that people rarely discuss these things until after they are already involved, and in this case, after the pregnancy occurs.
Because your bio-dad decided that he didn’t want to have a child at that time, nor to have a child with your mother, he decided to wash his hands of the whole situation. Although it sounds worse, it’s not that much different than a couple who puts their child up for adoption with the idea that they will never have contact with the child. You need to look at it like that.
Your bio-dad went on to marry and have kids with someone else. I’m guessing that he wanted to have kids with his current wife and that is what makes all the difference in this situation. Much like people that may have put a previous child up for adoption, then met someone that they did want to have children with. You may not like this fact, but it is reality.
Your bio-dad may come around some day, but don’t count on it. One of my cousins, now aged 42, was conceived, then her parents divorced before she was born because the dad didn’t want another child (my 49 year old cousin, her sister). So he left and never looked back. He ended up marrying someone else, having more kids and divorcing again. When my cousin was in her mid 20’s she looked him up, hoping to have the dream dad that she never knew. She met him and found out that he was kind of a bore and a jerk. She does not have a dream relationship with him at all. Although she did meet him, and she is on FB with him, the only thing she gets from him is forwarded jokes and pictures of cats playing the piano. He doesn’t converse with her and seems perfectly content to remain “out of the picture” so to speak. He didn’t want babies then and he doesn’t want an adult child now. My older cousin, this girl’s sister who actually spent the first 3 years of his life with this man, hasn’t had any contact with him since he left her mother just before her sister was born. She was hurt, angry and betrayed and knew he wasn’t a dream father. She has no interest in knowing him.
Now back to your situation. You bio-dad clearly didn’t want to have kids with your mother and wasn’t ready to be a father at that time and he decided to walk away. You have to put up with respect that decision. His other kids probably grew up not knowing anything about you. It probably came as a huge shock to them to find out about you. In a perfect world, these siblings would be thrilled and delighted to find out about you. In reality, they’re probably confused (because their reality is no longer what they believed it to be) and they probably feel somewhat betrayed by their dad (because he lied by omission and kept this information from them) and they’re probably angry at you (because it might feel like you’re waltzing in to take their father away from them or to butt into their lives) and they’re probably scared (because if you do come into their lives, for better or worse, their lives are going to change and they may not be mature enough or interested enough to want that).
I suggest that you tread very lightly and politely. You could write short sweet notes to all of them suggesting that you would like to meet them and open up the lines of communication, either now or sometime in the future. Then leave it at that. Don’t sit around pining away for something that you never had. This guy is your bio-dad only, he was never your father and never will be, even if you end up having some type of a relationship with him in the future. Don’t push it. Even if your bio-dad never wants to see you or have contact with you, your siblings might want to when they are older (especially after they become legal adults). But if they don’t, don’t hold it against them and don’t beat yourself up over it. Their desire, or lack of desire, to meet and know you have nothing to do with your personality or the type of person you are so DO NOT ever blame yourself for that. And don’t blame yourself for the situation that your mom and your bio-dad put you in. They were both young and they did what they thought was right at the time.
In the meantime, if you meet someone, have conversations about what you both want and what you would do if you got pregnant before you become physically intimate. Then live your life and be happy with or without the siblings and bio-dad. Your life didn’t, and shouldn’t revovle around this situation, it’s only a part of your life. Best of luck to you.