Hi Polyk2. Good on you for seeking advice and perspectives. I understand that it all must seem puzzlingly negative. It comes from a blend of negative personal experiences, reading of many other's negative experiences with the date-together-or-nothing approach, and weariness with seeing people make the same mistakes over and over.
I'm going to post below something I wrote in another similar thread. Apologies for the laziness of that, but I think it fits very well here. The only thing that may not be applicable is the stuff about asking your new third partner to be exclusive with the two of you -- if that's not something you would expect, feel free to ignore those parts. I'd be very curious to hear what you think of the rest, though.
As for how to meet people if not online, perhaps there are poly meet up groups in your area? If not you could consider starting one. Or you could just talk about your poly interests amongst your existing friends and see if anyone bites.
Finally, as for the question of why you can't stop thinking about this, some people really are just wired for poly and for compersion. If you fall into that category, which it certainly sounds like you do, then it must be incredibly exciting to finally be getting to a point where you could explore it. But I think your excitement makes this situation all the more dangerous... the higher you're flying, the more likely you are to project your imagination and ideal visions onto a new situation rather than seeing its flaws for what they are. Be very careful of that and try to stay objective.
I'm a bi female who's not in a primary relationship. A former aspring unicorn myself, actually (couples are hot!). I've been poly since I was a teenager, and have read a TON of individual accounts of poly escapades. And I would run, not walk, away from your proposition. I'll explain.
You don't want to date separately. So, if I'm involved with one of you I must be involved with the other. Yet, many new relationships don't work out in the long run. Some do, of course! If I started a new relationship with both of you, maybe we'd get lucky and one of those relationships would turn into an incredibly important love affair, something that imprints itself powerfully on our hearts and souls.
But wait -- that doesn't happen often. So the chances that it would happen with both of you are very low. Maybe I wouldn't end up feeling much chemistry with the other one of you at all, actually. Maybe I feel downright uncomfortable saying lovey things, or being physical, with the other one of you. But you don't want to date separately.
So now, in order to be with the new love of my life, I also have to try to force a connection with this other person, who may be perfectly fine as a friend, but isn't my cup of tea as a partner. What a weird, painful, and downright terrible situation I'm now in! If I try to break up with the person I'm not into, our closed triad is now broken, in your eyes. It's not your ideal anymore. You're disillusioned with it, or maybe just with me, because you had a goal, a vision, and it "failed." Am I allowed to date anyone new, now that I'm only with one of you? Can the other half of the couple even stand me being around, or is their heart too broken to be able to deal with my presence in the life of their partner? Am I now alone, without either of you, just for being honest, just for the sin of not falling in love twice over? At the very least, if I've moved in, I probably now have to move out. My life, on an emotional level, and perhaps a practical level, is now in shambles.
Of course, it could easily happen the other way around. Maybe I do fall head over heels for both of you... and for a while you think you're both in love with me too! Bliss! But then one of you realizes you're not in love, after all. You were in love with the idea of me, with the role I was going to play, the niche I was going to fill. But in reality, we just don't click. And now we're in just as bad of a pickle. Do you give up your triad-ideal? Or do you kick me to the curb and go looking for the next hot bi babe? Will that possibility be looming over my head the entire time we're together?
The above scenarios are just touching on the main problem with the triad-or-nothing approach. There are a legion of other issues, mainly having to do with power imbalance. For instance, this is supposed to be a closed triad. Let's say the three of us get together, but then an old flame wants to come back into my life, or a new friend wants to be more. You two have the wonderful reassurance and security of the settled comfortable love of your preexisting relationship, plus the terribly exciting, if scary, new love with me. You two got the choice to open up to adding another relationship to your lives when you felt ready. I only get the scary, exciting, new love. I'm not allowed to have a pre-existing partner, and I'm not allowed to follow up on any new opportunities, not allowed to make that choice for myself the way you two did for you.
You have a life together. It wasn't built for me, for my preferences, habits or hobbies. It was built for the two of you, and you've probably already done a great deal of compromising to make things work where you two differ. Now, on top of that, you're trying to fit me into that carefully-balanced dyad life, trying to wedge me into a space that you are opening up. It will almost certainly take a long time to make the adjustments that will make it truly work for me. It will probably take a very long time for it to feel like my life equally. It may well never. I may never "catch up" to the relationship you two have. It will all feel ideal and equal and perfect to you, because it was built for you. It won't feel that way to me. I will feel distinctly like the newcomer, the outsider, for a long time. But I'm not allowed to have anyone else. I'm not allowed to love just one of you, either. Is this a scenario where I'm likely to feel natural and comfortable, or where I'm likely to feel trapped?
I could go on, but maybe that's enough for you to see why this wouldn't be attractive to me, and why I would warn any potential unicorn not to consider your offer, not because you're bad people, but because I think the structure you're trying to form is an inherently fragile, flawed, and disaster-prone one. Not because triads can't work! But because if a closed triad is your only acceptable outcome, I am the one who is going to suffer, almost inevitably.
You may find a woman who takes you up on your offer. Chances are good she'll be younger, a bit naive, maybe not too independent, because that's the sort of person who is more likely not to see the disadvantages for them that are inherent in this. And, alas, her naivety and emotional immaturity will only make this more likely to end in disaster.
Does any of that make sense?