Perhaps a bizarre take on relationships: I've ONLY signed up for monogamous relationships with expiration dates.
My thought was, suppose I meet someone else I want to be intimate with? I'll only have to move on anyways. Best to just not get too involved and have an easy out ("I'm moving the country; I'm graduating college), rather than have to tell the person, "I just don't want to be with you anymore."
Now that I'm poly, I'm realizing, I don't HAVE to have an exit strategy. If I fall in love with another person, I can bring them INTO my life, rather than transition to a new life. I don't have to worry about getting emotionally attached. I can freely fall in love with my partner, and know that I'm never going to have to make a choice between them and someone else.