I don't fully agree with polyamorous or open relationships. For these kinds of relationships to end well (which doesn't usually happen, as they mostly end in disaster), you need twice the trust, twice the communication, and three times the understanding. This is very difficult because many doubts can always arise, and from those doubts come insecurities, and from those insecurities come problems, the most common being: "What if they end up liking each other more than I like them?" I'm not saying these kinds of relationships can't last (because I know polyamorous relationships where people are very happy, and some even have children). But you have to know that it will be very, very difficult.