Not knowing DH's backstory, and just taking this thread at face value, his summary of how he perceived that initial conversation (way back in the beginning of the thread) was a hell of an eye-opener. As many texts about communication relate, there is often a vast gulf between what one person says and what the other hears, and it is VERY useful to see what the other person has heard.
Again, just taking his raw reaction to what he heard (which, again, may be rather different than what was actually said--through no fault of his or hers, but only owing to emotional filtering), makes me more sensitive to what my own (mono) wife might be feeling. Admittedly, our situation is quite different, in that I've been bending over backwards "shoving it down" as RP put it, to give her time to process.
As for how people come to poly, well, I didn't "come to poly." I've more or less always been poly (married almost 20 years, not open at this or any time, and never cheated on my wife), but only recently stopped mistaking the desire for others (both physical and emotional) as a moral or character failing. I'd tried very, very hard NOT to have those feelings, and it simply didn't work. It's how I'm wired. I never once acted on this--I could not betray my wife's trust like that. I had the coming-out conversation first, and it was hugely painful for both of us. I never, ever attempted to lay down a "this is how it's going to be and here's how we're going to do it, hope you like circus life" scenario, and even now, I'm not sure that our marriage will survive. I want us both to be happy, but for now, largely for the sake of our son, I'm not pushing.
I am very, VERY pissed off at society in general, for the mono conditioning. I personally feel like the institution of monogamous marriage is a great big hairy fraud perpetrated upon NRE-laden young people who don't know any better. I mean seriously, who in their right mind lays down an expectation upon another that he or she will be able to satisfy their every need or desire for an entire lifetime? How bloody unfair is THAT? And then when, as most often happens, that expectation proves to have been a fraud, the person who believed it feels like a failure, for having failed to live up to what turned out to be an impossible standard, and there are seriously hurt feelings.
All of that could be avoided so easily, if we didn't grow up having mono marriage, "this is how you're supposed to do it" shoved down our throats from a very early age. Why shouldn't we be able to choose the forms our relationships take? Why shouldn't we expect those forms to change over the course of a lifetime? We've already seen in our own lives, as we transformed from children into adults, how the nature of our relationships changed, and in a very dramatic manner. What kind of stupidity is it that makes us think that change is going to come to a full stop as soon as we put metal bands on our fingers?
Yes, there are people who are mono by nature, and that's OK. There are people who, having examined their relationships, have consciously chosen monogamy. That's GREAT. That's the best way to do it. To fall into it because one simply knows of no alternative, however, is most often a recipe for heartache (I say "most often" owing to the high percentage of failed marriages and the huge percentage of cheating in mono relationships).
The vast majority, I think, of the drama and disruption that surrounds opening previously-mono relationships comes from all of the fairytale stupidity that we're conditioned to believe--ESPECIALLY that part about being able to be everything to each other for a lifetime. I think the lion's share of the hurt when one person tells the other that he or she wants to live poly is the realization that you CAN'T be everything to each other, and the sense of personal failure that gets attached to that. That sense of personal failure does not need to ever have been there, because the fairytale expectation should never have been there. The latter begets the former.
A sensitive, caring poly who values his or her existing relationship will take the time to let his or her partner come to that realization, that the desire for poly IS NOT due to a failure of the mono partner; it's the built-in, unreasonable and impossible-to-meet expectation that each of us will be enough for the other for a lifetime that is the failure. If that realization never happens, you part ways, as amicably as you can, and realize that's what you needed for each other to be truly happy.
I'm sorry if any of that was unclear. It's a burst that came to me earlier this evening, and it probably needs a bunch of rewrites.