If she considers you her "best friend" too it would be cruel to just spring a divorce on her.
As for the hookup sites, most of the responses from "women" are bots or women who work for the site. Adult Friend Finder is somewhat reliable but most of the other ones are just a waste of money. At least they were for me. Hope you had better luck.
At this point in my life I'd rather eat pussy for a couple of hours than fuck for a few minutes. Knowing what you can do well is important and comes with age (at least in my case).
When my wife and I were getting serious I told her I hated mushrooms, which I did. She told me that was going to be a problem because she loved them and cooked with them almost daily. Basically she told me "get with the program". So I tried them cooked in food a few times and fell in love with the little fungi. Now I can't believe I spent so much time hating them.
When I found Lush that was the first thing that came to mind, finding a FWB. However as I thought about it more I realized the fantasy was probably better than the reality. So now I enjoy Lush for all the fantasies that are described and talked about in the stories and forums.
I'd love to since my wife of many years hasn't had any interest in sex in many years. But I'd only do it if she was OK with it and the other woman's spouse was OK too.