In our case, hot wifing/cuckolding made life better for both of us. No more affairs, no secret life trying to satisfy otherwise unsatisfied lust or sexual curiousity.
I have a friend who pushed his (much younger) wife into cuckolding. They ended up divorced - I think there were maturity issues on the part of his ex. He has since remarried, he and his new wife are in the lifestyle, as swingers.
One of KK's inner-circle friends ended up divorced, her first husband ultimately couldn't deal with the jealousy aspect of her fucking other men.
That's the extent of my experience with impacts on relationships...