Cheating with my best female friend. I regret it, but I wouldn’t take it back. [M/F]

Sorry that this is INSANELY long, but this is more for me than it is for anyone reading, anyways :)

This happened quite a few years ago when I was 25. I had been dating my now wife for a year or so at the time. We would get married 4 years later. I've never told anyone this story until now. This happened with a friend a year older than me named Lindsey, who I don't think (hope) has told anyone either.