I've been married for 20 yrs. and it was strictly monogamous up until a few years ago. We were and would be again, quite happy that way, but we also like to enjoy the company of another girl from time to time, I'm bi and he's a typically horny guy so this works out great. Our girlfriends are single and we know they date others.
One girl really enjoys being with other couples mostly and she tells me tales of her escapades and I enjoy hearing how happy she is. Right now another couple she is dating is her ex-husband and his wife. We're all getting together in Vegas soon plus a few other single girls...it's gonna be interesting! This girl is awesome both as a friend and a lover.
Another girl we see has only dated other guys, I'm the only girl she's been with. She's one of my best friends and I'm hoping she finds a guy to settle down with because that's what she really wants. I know once that happens we won't have sex with her anymore and we'll miss that, but we want to see her happy.
At one time we were in a committed relationship (she was the one who said she wanted the commitment and we both cared about her so we agreed) with a woman who was going through a divorce, her husband was already out of the house. That relationship became too complicated and she was a scheeming, lying bitch. She claimed not to be dating anyone else but we found out otherwise. Lying is something we can't tollerate, and we knew she didn't practice safe sex. She was dumped. She begged and pleaded for forgiveness but we'd seen her lie to too many others and we knew she couldn't be trusted.
If you're going to fool around with more than one partner, truthfulness and safe sex practices are extremely important.
My husband and I do not hook up with other girls seperately, it's a 3-some when we're in the bedroom. There have been a few times when I've been busy and he's been with our friends for a little while, but that's with my knowledge in advance (like we're having a party and he gets a quickie while I'm in another room) and he gives me the same opportunities.
Our relationships with our girlfriends have lasted anywhere from just a few months to a year or more. We have a good time and it's hard to find friends who are trustworthy, so once we find one, we like to keep them as long as we can.