There was a brief period in my life, (a summer) where a girl and I agreed we didnt really feel like dating, we just wanted to boink. And thats all we did for the whole summer. Meet up on weekends at her friends apartments or a cheap motel and get funky.
As I recall the agreement was that we COULD see other people, but neither one of us actually bothered. Somehow we managed to build a trust with each other and one-night-stands with strangers (while enjoyable) isnt very safe. So eventually we agreed to be monogamous for the purposes of having safe sex. At the end of the summer she went back to school and I moved away for a while because of work. When I came back I got word she had moved back home after getting her degree.
So to answer the OP's question in a roundabout way: No. Because I never actually screwed around with more than one girl at a time, even though I had permission. That was not the last sexual relationship I had, and the few after that always seemed to last a few months with the implied understanding of monogomy for safety.