Hi friendlymum. I'm so sorry for your loss. You sound so unhappy, and I hope that this thread will help you.
Your post really resonated with me - my dad died 17 years tomorrow, and I spent the first five years after his death in a fog of grief. I blamed myself for not being there when he died (I was on holiday), for not standing up to his consultant, for not finding out more about his condition. I missed him terribly and couldn't get on with my life at all. Looking back, I must have been extremely depressed at that time, and it wasn't till I got myself some counselling that I felt the fog begin to lift.
I wish I had gone for counselling in the first year, rather than in the fifth - I was too proud to admit that I wasn't coping, and in a masochistic way felt that I deserved to feel this dreadful as a punishment for the things I blamed myself for. Counselling helped me find a way to forgive myself for not being there, and to understand that his death should not mean the end of my right to a good and happy life.
Please try to get yourself some help. It's not an admission of failure to do that, and if three years on your grief is still consuming you to the extent that you describe, that you have to do something in order to be able to create a different life for yourself, where your dad is still gone, but you are able to be happy again.
I still miss my dad after 17 years, especially now that I have two boys, who he hasn't seen, and would have been so proud of. But I have a good and happy life now, and that is what my dad would have wanted. And it's what your loving, supportive, wonderful dad would have wanted for you.
Hugs.