I am Shaken... What should I do?

My boyfriend and I were looking to have a and maybe even start a polygamous relationship. The thing is my boyfriend found a girl but she was more interested in him and tried stealing him away. We decided not to go through with it with her but now I am reconsidering the decision to start a polygamous relationship in fear of the same thing happening. Does anyone have any words of wisdom and should I just scrap the whole idea?