I’m sorry, that’s probably the worst way to find out. And you’ve been able to get very little information to give you closure.
It sounds like your family love you dearly. Your dad loves you, and that’s the most important thing. But it’s understandable to want to know your biological family – so it’s easy to understand the desire to keep looking.
Be wary; there may be very good reasons that your mum hid the truth from everyone – it doesn’t seem like there’s much information among your family regarding your birth father. I hope he’s someone worth meeting.