Hi op. I haven't read all the other comments, but just wanted to add my story. My mum didn't leave but my dad did. I was younger than you. I heard nothing nor had anything from him growing up. Neither did my mum (no CSA in those days). It really affected my whole childhood and I felt very different to my friends, it wasn't really the thing in those days to have no dad.
I met him again when I was 20 - I asked my mum to track him down. Turns out he was in the same city, very successful businessman, was on wife 3 but no other children. I met him and he seemed somewhat responsive to a relationship at the time which absolutely delighted me.
I now regret ever meeting him.
He has done nothing except bring repeated abandonment, rejection, mental torture and unnecessary suffering to my life repeatedly over the last 20 odd years. He has built me up with hope and destroyed my self esteem on so many occasions. I won't go into details, but his disinterest, outright rejection and cruel actions would begger belief. He has had an incredibly negative impact on my life.
I can honestly say that I would have been far better never to have met him. Perhaps you are better to move on with your life without your mum. I completely understand how it has impacted your life, but we can choose to focus on other things and actively use our past as a way of creating a better future. 