I can honestly say I don't (with all due respect) agree with the previous post PER SE.
IF one is already IN a monogomous relationship then I agree COMPLETELY with the last post.
However-I know and have been involved in relationships that didn't develop that way that are/were wonderful.
In my experience, if something is a "reoccuring event" in our lives-we are generally the "common denominator". What that means in regards to THIS situation is that somehow you are the pivotal piece that is somehow creating a dynamic that leads to this repetitive breakdown in your relationships.
THE GOOD NEWS about that is that it means YOU can change it!!
The bad news is that like much of everything else-it means some DEEP, HONEST soul searching.
People tell me all the time that friendships created in our school years don't last into adulthood.
I'm 35 years old. My 3 closest friends have been in my life 32, 22, 17 years respectively.. the next 3 are 14, 12 and 7 years respectively... so OBVIOUSLY it's not that they DO NOT last-it's that people don't MAKE friendships that last.
My whole life I've always "sensed" when something was deeper between myself and another person. And those people I catered to the relationship. A person has needs, but a RELATIONSHIP has needs also-and the needs aren't always the same for the RELATIONSHIP as for either party in it.
It sounds (you haven't said a lot here so if I'm wrong I apologize) as though you are creating relationships with people who aren't interested in LONG TERM HIGHLY COMMITTED relationships. Of course there are LOTS of those types of people in polyamorous circles, there are LOTS of those types of people in monogomous circles as well.
BUT-there are many of us who REQUIRE the long-term, highly committed relationships IN POLYAMORY as well. Some of us are just not as fast to "jump in" to sexually involved relationships just because the "chemistry" is there because we want more than just the chemistry.
Maybe you are taking offers that don't REALLY fit what you are looking for?