Hey, demanda, and welcome! In all my attempts at advice, please tell me if I'm off-base-- I'm replying late at night and it's hard to feel people out from a few short posts anyway.
I hear you saying that you're very open with your partner in a relationship that you value highly, and that the mere suggestion of him thinking about poly scared you enough that you considered ending it. I'm happy to share what poly is for me, but I find myself wondering more about what you're afraid of. In my experience, saying fears aloud tends to rob them of their power, and clears the air to hear what is actually on the table. What's worrying you so?
See this is what I don't understand about polyamory. Isnt it supposed to be about having it all? I dont want to be owned by someone, but want to be so special and connected to someone that they take that risk with me. It seems like there are plenty of married couples that engage in it and are happy. Can I hear from some of them?
For me (about to be in a married couple), and I can't speak for anyone else on this, being poly is about having the relationship that makes the most sense with each person in my life. Right now, this means that I have two life partners, an "it's complicated" girlfriend, a bunch of friends with benefits, and a close friend on the horizon who's about to fall in all somewhere... If I were monogamous, there would be rules about how I could relate to each of them: this pairing has to be sexual on a regular basis with the goal of purchasing a house, this one has to be about book-swapping without any flirtation whatsoever, etc. I much prefer being able to let each relationship develop in the way that fits the people involved.
The whole notion of "having entanglements" is a consideration, but seriously, someone throwing that out there just lends itself to the perception most have about polyamory that I know of- that it is immature and irresponsible and the core comes from being brought up around a dysfunctional family. I would like to believe that there are many different ways to define a healthy relationship. Honestly that type of insight to this lifestyle seems narrow and juvenille.
I think what Mono meant (correct me, Mon, if I need it!) is that marriage and bearing children are both huge responsibilities, legally and financially and socially and more. It's better to go slowly, no matter your lovestyle, when heading toward a big decision, so you can make sure you're doing what's best for the people involved. In poly, that can lead to slower decisions, because there are more people involved. You might not like the word "entangled" (for me it conjures up images of the vines around Sleeping Beauty's castle), but it certainly describes the way a bunch of people caught up in each other's lives can be. In my case, most of the people who are seriously involved in our constellation (sexual or romantic feelings expressed on a regular basis) are co-housing together, along with some platonic friends. We actually have to buy groceries and do dishes and pay rent together, so we truly are entangled, and I certainly wouldn't call it immature, dysfunctional, or juvenile.
It might help us help you if you described what you imagine polyamory to be like. We'll probably just tell you if we've been in similar situations, and what sounds healthy or unhealthy about what you're describing, but it'd give us all more solid footing.
Thanks for sharing, in any case, and good luck with your partner. Keep posting-- we're here for you.