I'm so sorry this has happened at such a young age for you, we do understand. But it is never easy at any age. My alcoholic Dad died in his 80's after being incarcerated briefly and sober for 3 years, he was in late stages of Alzheimer's. I too felt immense relief. I did many years of grieving for the Dad I never had so it wasn't a shock. Let yourself grieve how you need. If you don't cry that is fine. Don't expect any "normal" reactions and don't punish yourself if you feel you are coming up short. Let it play out however it does.
I'm glad you now understand that your relatives couldn't have any more wrong with their blame on you and his drinking. There is no reason you could have supplied that would be the fault of his drinking.
As you work through your feelings you might want to read the "stickies" posted above if you haven't already. Saying a prayer for you.