I know of a few couples (some who've been together for over 15 years!!!!) who experiment. Sometimes including a third boy or having an arrangement where they can fuck with other men but always come back to each other.
Then i know one guy who is dates a business man who travels a lot and he's a total bottom but is seriously a "one boy boy" so he has immense collection of sex toys to keep him happy. I think its incredibly sweet.
They're all incredibly satisfied and don't complain about the lack of sex or the wandering eye of the partners. Whereas a lot of my straight buddies who are tied into that traditional norm of sexuality constantly moan about the sexual breakdown of their relationships. They don't understand that it isn't always about slutdom vs relationship. My gay mates have proven to me that with a lot of understanding you can have achieve what you want with your partners. It isn't always one or the other. My gay mates have merged slutdom into their relationship.
Maybe one day, if i find "the one" but the practicalities of life get in the way i hope that i come to some sort of arrangement that actually allows me to have my cake(cock) and eat ALL of it. :-)