My DH foresees being in your biological fathers position.
His ex had an affair, married the OM and then did everything in her power to stop my DH from seeing his son. My DH was military and on deployment for more than half of every year and if contact isn't facilitated by the resident parent it is not possible to maintain it. She threw away his letters, hung up the phone and denied him access and called the police saying he wa threatening if e visited. His son forgot who he was and so he gave up trying because it was more damaging to his son to keep going with attempting to have a relationship.
She did this because she had her neat little mum and dad family with her and OM bringing up the child.
I am 100% certain that us NOT the story my DHs son will hear. He will be told nothing at all and if pushed mum is highly likely on past form to say he abandoned them, was violent and abusive, threatened step father (which he did when he caught him in bed with his wife!) and he should stay well away. And I'm positive son will believe every world because why wouldn't he?
You do NOT know the whole story nor will you unless you meet your bio dad. Maybe he is seven shades of shit, maybe he was then but is now a decent guy who wants to see how his only child turned out and see you before it's too late.
My DH went looking for his own bio father when he was mid 30s and when he found where he lived he was too late - his bio dad had passed away the previous year. It's a huge regret for him he never got to meet his real dad and his half sister tells him his dad looked for him for years before he died and was always sad he never found him.
Maybe your bio dad is feeling his mortality and wants to meet you before he passes away.
You just won't know though if you ignore him.