This is a friendly forum with lots of engagement but that's a two way thing. You'll see most of us, whose names aren't in our user names, signing off our posts with our first names.
Just stop posting, log out, and there you are. This method doesn’t break any topics you might have posted in, because your posts will remain frozen in time.
You could contact @adrian who owns the site and ask him to properly close your account if you like.