monogamy is natural and the way to go, in my opinion. in an ideal scenario, one goes on dates and settles down in their late 20s/early 30s when theyve found someone.
polyamourous relationships might work for some of the mormons, but they are a special exception. theres a documentary on it somewhere... in it, a man was married to at least 7 women (i cant recall the number) and had many children with them. he worked it out that he would share a bed with different one each night. the women were not jealous of each other, but they had a unique religious mindset about it.
unless your friend is a mormon, forget it. it is doomed to fail. anyone with a modicum of self-worth should never split their time with their loved one.