Stop beating yourself up. Many people lead sad, lonely, painful or unfulfilling lives. Many people are married with happy families, comfortable lifestyles, good job, nice holidays, friends, all the trappings that anyone could ever hope to achieve - but are bored senseless with their lives.
You think you made bad mistakes? Join the club. Only the very lucky few get it right - and even then, adversity can be lurking just around the corner for them or anyone.
As far as separations, divorce and ruined marriages are concerned - do you realise how oh so very common they are? Marriage can be a warzone that doesn't take prisoners. I know so many people that have gotten divorced, having enjoyed seemingly blissful marriages previously - and let me tell you, there were no fun 'games' involved on the way down, no 'experimenting with exciting lifestyle choices', no 'pushing the threshold of conventional, mainstream conventions' just pain, misery hurt, anger, suspicion, distrust, jealousy and non of the pleasure.
With you and Leah, at least you were trying exhilarating, out there stuff, more excitement packed into a few years than some people enjoy in their entire lives. Think about that. And I'm not being a 'cheer leader', as some would say (and anyway, I'm not sure you can cheer lead an event that is already finished!). Leah got to experience some mind blowing sex that would never have been in her life, unless you had opened the door for her. You have very well and explicitly explained what you got out of it, that so many on this forum can easily understand, sympathise and empathise with. Many here would love to have been in your shoes, but have never had anything like the opportunity and can only dream about such things by reading accounts like yours.