There really isn't much I can say. Lost my dad when I was very young. I'll spare you the details.
What matters is what you do now and the immediate future. Try to remember all of the things you loved about him and otherwise as well. Share stories and memories with his/your family and friends. Did he have any phrases he liked to use and which came to identify him to some extent.
I'm not doing a very good job here, but try to remember all of the things you loved about him as well his own personal "style." And bring as many folks in on that as you can. You'll laugh at some things. Cry at others. and by the end you'll be exhausted. But it will be a good tribute that helps to reinforce the good memories and let all of the ugly shit go to where it belongs.
If you were very close, it's going to be a rough couple months to start. I wasn't really close to my mom because she was more of a governess than the stereotypical mom-type. Of course we loved and cared about each other, but any sort of overt emotion we tried to avoid. Too icky.
She died of a stroke so there wasn't really much warning. If I could have talked her into getting some sort of health monitor, they probably could have saved her but that wasn't to be.
The biggest thing though, don't blame yourself for whatever things you regret, if any. Criticizing yourself after the fact accomplishes nothing. Forgive yourself first and then if necessary, forgive him.
Sorry this is kind of a jumbled mess, but everything is going to feel like that for a while