I agree with you Sage when you say that a good understanding of poly will help the jealousy feelings.
I also believe that a whole lot of talking with deminsh those thoughts and feelings also. The three of us have talked until we are blue in the face about anything like this ever coming up. We all three promised to each other that if any one of us ever do feel this way, no matter what the others are doing, they will stop in their tracks and talk to the person feeling outed. I know I never want my husband or my girlfriend to feel bad in any way, and if I can prevent it I will. Lucky for me they feel the same about each other and me.
I'm a big talker. I think if you lay it all out there, have no surprises, etc that you can get through about anything. I have to be mentally preped to deal with certain things. I'm weird like that.