Kids of parents who were never there?

My 'dad' left when i was around 6 weeks old. My mum met a new man a few months after and he raised me as his own. 15 Years on there still together and i call him dad and don't even think about the fact he isn't. Mine and my mum have a reasonably close relationship so if I did ever want to meet my biological dad she wouldn't mind arranging it etc. Although I don't want to and doubt I ever will after he left me and my mum and my older brothers and sisters. Hope I helped :) x