I've been thinking about this a lot recently. I've name changed because I am very aware that this makes me a horrible person.
Me and DH have been together 10 years and initially had very similar sex drives. DH is 6 years older than me so not a huge gap. He then became less interested in sex as the initial spark fizzled a bit but I didn't. Rather than be a reasonable person I toyed with the idea of an affair. Over the course of a couple of years I went from playing with the idea to speaking to strangers online. At one point I'd got as far as arranging a meet up with a stranger.
First and foremost DH obviously didn't deserve me behaving this way. If it was that big a deal for me I should have just left him. Secondly this would have been horrendously dangerous, I was a young woman meeting a stranger at a hotel. Thankfully I saw sense and cancelled.
This is all around 7 years ago now, we are both happy (I think). We have a wonderful son who is 1 and although my sex drive is still a little higher than DHs it's not something I think about often and I certainly don't chat up strangers online anymore.
I do often feel guilty though, DH has no idea that this ever happened. He worked long hours and I was often home alone so he was never suspicious about me being on my phone or anything like that. I knew what I'd done and I still agreed to marry him, married him and then had a child with him without being honest.
I feel like I should tell him but I don't want to risk ripping us apart for DSs sake and selfishly mine too. I've just made such a mess of it and if I could grab my younger self and give her a slap I would.