Have you thought about going to a bathhouse?
While I am well aware this is probably the scariest thing you've ever thought of, really, it's quite different. And I'm sure there are some very nice bathhouses in London. In US, my favorite is STEAMWORKS in Chicago (look it up!)
The only fear you will experience is the drive to the place and the walk to the door. DO NOT FEAR. You will be greeted by a very friendly guy at the window who already senses your fear. He will introduce the club rules, and direct you where to go.
Once inside, you will find all kinds of guys JUST LIKE YOU. Go to the lockerroom and wrap a towel around yourself. Walk around, check things out. You will experience men in the showers, men wandering the halls, men in the sauna and the dry sauna. Roam the halls, look in the cracks in the doors. Men love it. Flirt, wink, be playful, look stare, respond to others' flirts, winks, stares, etc. With an ass like yours, you will have NO problem appealing to others. And it won't be long before you feel like you are right where you belong. Try it out. I've met MANY married/bi men at bathhouses (most of them have wives out of town). Any questions, just respond. I'd be happy to help!!