Straight Guy With a Gay Fantasy

Yeah, so maybe I'm not as straight as everybody thinks I am.
I grew up as the middle boy in a family of five boys. If you think we all kept our dicks to ourselves until we started meeting girls - well, that didn't happen. I've sucked every one of my brother's dicks and they've all sucked mine. I'm sure we've all licked each other's asses, too. My oldest brother even liked to let me fuck him in the ass.
Jump ahead: I've been married forty years. Raised three sons. Got in trouble early in my marriage for fucking my sister in law. Big football fan. Go to church sometimes.
That's the background. Over the last 10 years or so, my wife has completely lost interest in sex and right now, I can't even touch her.
Her little brother, who had been homeless, living halfway across the country, moved in with us last November. Now, I just retired and he's 58, but he qualifies as a little brother since he's about 4ft. 11in. We all get along great.
But his is an interesting story. He and my wife talk a lot about when their older brother and his friends would take - let's call him JB - on camping trips and take turns fucking him. Now, he's been married. Has some kids who don't seem to talk to him.
But he has said some things that make you wonder. Particularly when he's had a few beers. He was asking what he could get me. Along with beer, coffee, a sandwich, etc. He mentioned sexual favors. Said he doesn't want to try to work around me in the kitchen, "unless I'm feeling gay." I heard him mention to my wife about a time "before I liked having things in my ass.
If you're still reading, this all brings me to the following fantasy:

I've never said anything to JB about the state of my marriage. Unless my wife said something to him, he knows nothing about the fact that he's gotten laid since I have.
So we're in the garage trying to get the place organized. He's told me a few times what a great guy I am. He obviously likes me, and he's used to being taken advantage of. Strangely, he would be happy to have me take advantage of him as something of a gift to me because not very many people have been nice to him.
Somewhere in our conversation, I mention my sexual frustration. Of course, we're both drunk by now. In my fantasy, he turns to me and says "Well, hell. You can fuck me if you want."
It will surprise him when I don't just wave him off like I do when he says weird stuff in front of my wife. I would stop. Meet his eyes with mine and go "Really"
"Sure, why not. Everybody else does."
"Right now?"
Remember, he's drunk. Now I still haven't committed, so he's going to feel challenged to commit and at this point he'll be undoing his pants and pulling them down while planning to get on his knees on a coffee table we have up against the wall.
I'll warn him: "If you get on your knees there, I will give you the surprise of your life." Of course, I'm taking my pants off, too.
Spurning my warning, or perhaps being exited by it, he gets on his knees on the table top with his tiny little asshole pointing right at me, ready to receive.
At this point, I drop down on my knees and bury my tongue in his asshole. The fun part is knowing that this is the last thing in the world he expected.
At this point in my fantasy, I always think, "fuck, what are we going to use for lubricant out there?" I'm going to need to sneak a tube of A&D Ointment out to the garage. At which point, this quits being a fantasy and starts becoming a plan.
I pulled my pants off the same time he did his. While I'm eating his ass, I get the tube of A&D Ointment out and stuff a big glob in my asshole. Then I reach around and rub what's left on his hard cock. If it isn't hard yet, I'll make it hard.
Then, I'll grab his little waist and pull him off the table. Grabbing his dick as fast I can. While holding onto his dick I'll climb up on the table and pull his dick to my asshole.
I like having stuff in my ass. I've used carrots (they're awesome straight from the refrigerator), vibrators, miny baseball bats. I even have a stainless steel mortar and pestle set that's fun. But I've never had an actual dick in there. We'll start slow of course. But I'm really looking forward to feeling his hips slam into my ass while his dick slams into my hole.
Once he's cum in my ass, I'll be happy to fuck him if he really wants me to. But I think I'd rather have a blow job.