Thinking of cutting out a toxic parent-not sure I can

Hi, this is my first time posting here. I'm sorry if this post turns long and rambly but I need to get this out and I'm not sure what to do next.

I (29f) am currently not speaking to my dad and am considering cutting contact for good. The event leading up to this seems a bit trivial but it has been the latest in a long line of issues. My relationship with my dad has always been rocky to say the least. As a child he terrified me and my sister. He didn't seem to understand how to care for little kids and had no patience with us. If he tried to teach us anything and we didn't get it straight away we would be in for name-calling and shouting for a pretty long time. He liked to drink (and still does) and would come home either in a screaming fury or would be the life and soul of the party, making promises that would never materialise. He was never physically abusive but some of the horrible things he could say still makes me cringe now. I also remember thinking that it was normal to have parents that shouted at each other all the time. I have some good memories of him but they're heavily outweighed.

Fast forward to the present day and he seems to have mellowed somewhat. Now my sister and I are adults it seems he can talk to us easier and he likes that we can drink with him now too. It was his 60th birthday recently and my sister and I wanted to do something special for him. We ended up buying him tickets to see a certain singer who's been touring in the UK recently; we knew my dad is a fan of their music. My sister and I house-sat while he and mum went to the concert. They were back 2 hours later and it turned out they didn't stay because he didn't want to. The full story is too long to put here but it was apparently for many little reasons such as them not being able to find the car park they wanted, arriving too early for the show etc. My mum wanted to stay but there was no way she could once he made his mind up.

So my sister and I have had our time and money wasted and what we thought would be a lovely gift thrown back in our faces. We were both livid, but my sister has since forgiven him. She lives a lot closer to our parents than I do and is very emotionally dependent on them. However, Dad has not contacted me since (we didn't speak to each other that night either) and hasn't apologised. He's told my sister that he feels there is no need as he has already said sorry to her.

I tell myself to carry on with day to day life but this recent situation has just bought home to me how little respect he has for my feelings. It's not about the money, but the fact he can't even bring himself to apologise and feels he doesn't need to. It makes me feel worthless. I realise how he's never valued my interests or the work I do. He's not interested unless it's something he can relate to directly.

My mum has said that she wishes she left years ago but she won't leave him now as she feels too old to start again, and that despite the problems over the years she feels comfortable and is financially secure.

I don't want to feel like this anymore. But despite all he's done, I feel horribly sad and guilty at the thought of never speaking to him again. My sister is saying I should forgive him this because 'he's our dad'. I don't know what to do for the best. I feel blessed that I have a wonderful partner and I love our life together. But I feel torn and stuck.

Thank you, hope you are all having the best possible day x