It seems that you have certain, perhaps limited, ideas about what polyamory is and what polyamorous relationships are supposed to look like, as if it's the same for everyone, across the board. You really can have just about any configuration you can dream up. But it starts with the people first, not the role or title. If you meet someone who really floats your boat, that's something. Then you see how they fit into your life, and they see how you fit into theirs. If you stay very fixated on finding a life partner to marry someday, then you could miss someone totally fantastic for you right now.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein