For some of you that know me, this might be surprising, but I have known/met many people who were in poly relationships, sometimes being friends friends with multiple people in one. Anyways, none of them ever work out well, usually a big problem is that on person gets left out, it's impossible to divide your time/attention with more than one person equally, and so jealousy arises. I have even warned people going into poly relationships about the dangers and they have either ignored me or taken the advice and still all had the same outcome, me being right as always.
Anyways, the short is that it I have never seen a poly relationship work out.