Pana, any guy who would cheat on you ain't got a full deck anyway. And if he was out scouting other talent, how perfect could he have been? Since you got "mad" about it then I'm guessing you were not into the "sharing" thing.
I suppose if the ground rules are explained up front why should it be a problem? Just make sure they understand there are no strings and no committment to anything. As attractive as you are, and with what sounds like a great personality, Im guessing you have no problem with getting dates. I bet there are a lot of women who want to do the same thing as you. Society and mores place a different value on folks our age doing the "teenage dating dance". Teenagers are expected to be "flighty" but when we get to our age, its epected we are much more stable. IMHO, keeping a man interested in a "shared" relationship is going to be almost impossible. Especially when there are so many others looking for stability and committment. Good luck, I hope you can find what you are looking for. Just my 2 cents. Adam