I don't think anybody mentioned this specifically yet, which surprised me, as I often see it mentioned on threads about adding another partner to an existing couple.
"we decided we want to share our relationship with another woman"
I don't know if you think about how that comes across, or if you are projecting that attitude to women you are meeting. I understand you don't want to date separately, but this is the main sort of sentiment that will keep you from finding what you seek. It may be a reason you are attracting the sort of people you are. ALSO, I will just point out that you talk about making a solid connection with somebody after a week or two...it takes longer to make a solid connection, and I hope you've figured that out after the experiences you talk about.
You don't share relationships, it's not an umbrella or a bottle of wine. I hope you've read on the forums (I imagine redpepper would jump in with something like "search for tags with triad, polyfidelity, etc") Read a lot about how its three different relationships. You might even be more likely to build a successful triad if you are willing to date on your own, just women, or to just build friendships independently at first.
It really struck out in the initial post how many "we this" "we that" statements there are. I do strongly urge you to think about if you're coming off as either co-dependent, or giving off a vibe that just screams "we come first!". I'd date both people in a couple if I was interested in both of them, but I'd never date a "we".
Happiness will never come to those who fail to appreciate what they already have.