How to tell a story you've never told

I'm 21 years old and I have never told this to anyone... My dad is an alcoholic and has been all his life. He has never been abusive or hurt me physically in anyway which makes things a lot harder. However, i have always felt like he never truly loved me because alcohol was in the way. My life has always seemed to go up the hill i used to hate knowing my dad was drinking although i never knew he was ill. Addiction is an illness i understand that now but years ago i didn't. When he drank he used to gamble and we would always be in debt. He got cancer about 6 years ago however this didn't stop him. He was very lucky to survive and be cancer free but after all that he is still drinking. Because of my dad my mum is very emotionally unstable. She has been with him for all these years and after everything he has put us through. At first she used to argue with him or just let him drink to have peace she helped him pay all the debt which basically supported his addiction. We first realised my dad was an alcoholic about 5 years ago. There was a lot of arguments tears but my mum just let it happen. August last year my mum decided that was it she didn't want to go through it anymore and decided to leave my dad. However, because of all that alcohol she walked in on my dad trying to overdose. After that incident my dad decided to get help. He stopped drinking for a year. Things seemed really good, i felt more relived i felt like i always carry this pain with me and i still had that fear of him starting to drink again but i was hoping that would never happen, but how wrong was i? very very wrong. About a month ago my 12 year old brother said to me " I think dad is drinking again" my heart sunk and i felt like my worst nightmare has just hit me. I didn't want to accuse my dad of anything hence why i started looking for any bottles anything i could find to prove he has. i found nothing. he was always really good at hiding bottles but one day i was sat talking to him and his eyes were shining just like they used to when he drank and his face seemed more red then usual and at that moment i knew this has started all over again. i decided to tell my mum because i felt like that was the best thing to do. She was devastated as she also thought he has and i just confirmed her worries. She told my dad straight away she doesn't want to be with him however she has said that many many times and never done anything about it. She seems pretty serious now which is very scary. The issue is that my dad still thinks hes not an alcoholic. He is a normal person who likes a drink and that's what it seems to him because he works he socialises. As a family we "look" normal but we are very far from it. I always dreamed of having a normal dad. I always wanted to be daddys girl but that never happened. i do believe my dad loves me i just think he loves alcohol more. He is now drinking full time again still in secret yet hes not an alcoholic although he will not put a glass of wine on a table in front of us... All these years i've always felt different. I lived to please people, i have huge attachment issues. it's all or nothing, i worry and stress over the smallest things and i am only just realising that this is why i am the way i am and i hope that one day i will truly feel happy because i could never enjoy my life the way i would like to. However now if my mum and dad split up i'm just worried about him. i'm worried he will do something stupid i know i can't control it but how do i live with myself knowing that there is nothing i can do?

For all the 21 years i have lived i have never told anyone about this. I always felt ashamed. I still do although i know its not my addiction i just seem to struggle to come to terms with it fully.