My life has been similar to this over the last year. Well, I actually was in a triad with a married couple that turned into a vee with the male being the hinge and the wife, pretty much, being of the same mindset as Eric. In the beginning of our relationship, when we were still a triad, the wife became pregnant and we were excitedly preparing for that. Unfortunately, the pregnancy resulted in a miscarriage a few months into it. A couple of months later, our relationship changed from a triad to a vee.
All of your concerns are valid but I believe if you just continue to communicate your concerns, communicate in general, and continue to be genuine, involved, and loving ... things will be clear and everyone will be heard and each circumstance can be worked through as they arise.
I look forward to watching your journey.