If you can make it work with one other person and have a fulfilling, understanding and well-communicated relationship that gives you both a feeling of reward and healthy challenge to achieving goals for both of you, you have accomplished one of the most challenging aspects of life. It's very hard to share and open your life with another person, that person also has to be on-board with the same goals and plans. It can take a lifetime to really fine-tune a good monogamous relationship to the point that you're both functioning smoothly with each other.

And if you can do this with TWO other people, and those people ALSO can do this, that's not just an accomplishment, that's a sign you should probably buy some lottery tickets, or you're actually the protagonist in a generic anime or manga and you don't need to worry about the girls because some kind of space monster is probably going to try to kill you.