Just been through exactly the same thing with my Dad. He was the same age as yours. We lost our lovely Mum unexpectedly and he was lost.
Its okay for people saying encourage him to get out and get hobbies etc but my Dad just didn't want to. No amount of encouraging would get him to go out because he didn't want to go anywhere without my Mum. It was really sad. Over time he got less sad but he was very lonely. One thing that helped my Dad was their dog. He had to go out each day, at least for an hour, to walk the dog and the dog was a great source of comfort to him on days when neither myself or my sibling could get to him to spend time with him.
One way I looked at it was yes, its inconveniencing my life for now, and I don't want to have to care for someone but he is my Dad. My Mum would have wanted us to be there for him and help and support him as much as we could. And after everything he did for us, and the things he gave up for us, I felt it was my time to give back and I knew it wouldn't be forever.
People on here saying he is being selfish. Yes, he is. But he can't see past his own loneliness right now and he is very obviously still grieving. Losing your life partner is a massive trauma and grief isn't linear. My Dad pined for my Mum everyday and he existed, rather than lived, without her. We did our best to help as much as we could.
Saying that though, you do need to try and carve time for yourself and try and find some compromises somewhere so you are not unhappy and unfulfilled yourself.
I mirror other peoples opinions in that your siblings are not far. They have to do more to keep him company and do their share. You have TWO other siblings who should be sharing the load a little more and take some more off you. Please sit them down and discuss it with them and come up with a plan that is fairer on you.
Just to say, love him while he is here. My Dad passed away suddenly in his sleep one night. We had no idea the last time we saw or spoke to him would be the last time. Like your Dad, he was well, fit, independent and still driving. He had been well. He was alone when he died and I hate that. But at least he died and I have no regrets and I know I did my best for him right until the end and I know how grateful he was to me for this.