Being in an exclusive relationship reduces the chance that your emotional (and sometimes finical) security is safe. Declaring a partnership with a label comes from a fear that it can be easily broken by an outsider. However, if you accept that love isn't something that can be controlled or contained, that people and their feelings can chance, I can see that polyam would be a more emotionally mature state. But thats so long all parties communicate without deception to theirselves or others about their intent. I had a friend who's SO wanted to be in an open relationship but it turned out to be just an excuse to cheat on them without feeling so bad about it.