How do I deal with my old man who won't stop talking?

My old mans a trooper. A bloke who has lived, so far, a very colourful life.

He doesn't have dementia, more like he has the opposite of it. He seems to remember every little detail of his life. Ever since he had a stroke on the hospital table for an aneurysm, his memory has become video perfect. As if events only happened yesterday. This means he has 5 versions of every story, all true but told differently from different angles. This translates to pure mental torture to anyone he comes in contact with. Namely me. He's nearly 80, I have a family of my own at 30. He comes around quite often, to the extreme dismay of my partner. The kids love him and he loves them with a fierce passion. Even though I have many siblings, he has attached to me. I was his mums (my nans) favourite grand child for reasons I can't be bothered explaining and I think this also translated to my Dads opinion. Therefore, I'm the one he seems to have a passion for spending time with.

I'm writing this from my phone so apologies for grammar.

Anyway, my Dad is so intertwined with getting his stories out that he will keep talking even if I'm not paying attention to him. Like even right now he is deep in conversation with me where he is the only participant. Whether I face him or not, the detail and effort in what he is saying is the same. I feel bad that I cant always have the mental energy to soak it all, but I just cant do it. After hours of non stop (1 way) chatter, I feel like crumbling.

I want to get across that i love him so much that even thinking of not having him here on this world even for a brief second, brings me instant tears. I cant imagine not having him. I still hope that humanity will find a cure for ageing before he decides to leave.

My partner just avoids him when he visits, so theres no sharing. "He's your father, you deal with him."

I dont talk with my siblings (they're toxic, save a couple) and they live far away. Whenever my Dad tells me on the phone that he's coming the next day, my heart falls into a dark abyss. Even though its expected, I still feel the mental anguish to come. Out of 14 days he is here for 2.5 of those, it might seem like only a small amount but after years of this its finally starting to break me and I'm reaching out for help.

He has a hard working mentality so when he visits, its time to work. Working in the gardens or whatever other projects I allow him to do. We do it together, for the most part. If I get tired he simply continues by himself til he gets over it and decides to start talking again. I then go to my normal night shift the same night. Also physically demanding. It's the mental work that gets to me though.

I love his stories, and he teaches me so many things. But recently, maybe the past 6 months, I feel like I'm burning out.

He still lives at his own home, does his own things and has his own family (my step mum). He hasn't had a good run with partners.

I must reiterate, he doesnt have dementia. He has the opposite of it.

Any help and advice is appreciated. I can answer questions if I can. Im not sure how these forums work.