I hadn't spoken to my dad in eight years and got a call that he was in a hospice in my hometown and wasn't expected to survive the weekend. I drove up, feeling that if I didn't, I might regret it. He wasn't a bad dad in a lot of ways, just very strict when I was growing up, and made me choose between my family and a boyfriend he didn't like. I chose the boyfriend.
When I got there, he was really ill and in a lot of pain. I stayed there for 36 hours (he was mostly unconscious) and held his hand when he died, because I don't feel that anyone should have to die alone if someone, anyone, can be there.
The following year was very confusing - I grieved for the life we could have had, I was angry at him, and at myself, and it brought back losing my mum twelve years earlier. I chatted to a psychologist at work about it, and he said the important thing was to not think "what if?" Whatever happened, you can't look back, you can't change what happened no matter how hard you try, you just have to look forward.
And my dad was right - my boyfriend was a selfish narcissistic man. My experience taught me that you don't stop learning when you leave school, you're learning all your life and sometimes not getting it right every time - both me and my dad made mistakes. Grieve if you need to. You'll know when it's time to move on. You still have lots of life to live - make the most of it.