I was absolutely enthralled by this and fantasised about it a lot. I would jerk off while thinking about eating another man's cum from my wife's freshly fucked pussy, or sucking her lover hard before inserting him inside her. It was a slow transformation, to where I soon began imagining myself injected into the whole scenario. It was fueled by reading 'Hot Wife' and 'Cuckold' stories in various forums, like Literotica, and watching whatever porn vids that were related. My fascination of imagining her having sex with other men did not end there. I accepted her explanation, even though I wish she had taken me up on my offer of being free to play around. She rejected the idea straight away and insisted that she had just lost interest in sex, not in me.
I tried to coax her into some unconventional avenues, like having sex with other men, if she wanted to. My wife and I had an active sex life until about 7 or 8 years ago, when she became very disinterested in any form of sex. I am 67 and happily married for over 40 years.