Dear OP
Sorry to hear that. I truly understand how you are feeling because both of my parents are gone. I wasn't even 18 years old yet when my Mom died and like you with your dad, I walked in one day and found her on the couch. As soon as I saw her I knew what happened.
Having gone through this myself, I know there isn't allot I can say to help other than a year from now, it will be a bit easier to handle but you will still miss him as much as you do right this minute.
You will have dreams about him and in them you will still be able to be with him and hear him talk and it will be just as if he were still here. I have lots of dreams like that about my parents and it makes me happy because I get to hear their voices and I get to hug my mom in them.
Surround yourself with your remaining family and hug them and tell them you love them every single day. I wish you all the best.