I think that's the case of relationships in general. I notice everywhere around me that some people are just not good at relationships, be it with one person or more. I guess if you put in more people who are bad at it, the results can be more catastrophic. On the other hand, you might need only one person who is good at it to "train" the others, too.
Me: 31F, straight
Seamus: My husband, 32M, straight
Dragon: My boyfriend, 29M, pansexual, married to Fox
Fox: My boyfriend, 29M, homoflexible, married to Dragon