Just to be clear, I really have no problem with being a secondary (or even a standby, if that's what was right for that particular relationship), provided the nature of that relationship has the ability to develop on it's own merit. With this new relationship that I'm exploring, many people would see it as a secondary relationship. At this point, I'm not planning on living with him, I'm certainly not going to be having kids with him though I do want to have kids at some point and am actually going to be moving overseas in a couple of months. However, what I really like is that our relationship is developing into what it can and should be for itself. There is no "protecting" his other relationships in this situation because all of the people involved have a high level of trust and understanding that everyone will make choices that honor each other.
I get it. I do. I'm a HUGE fan of letting every relationship evolve into what it might be.
On the flip side of that, knowing I agree with you quite a bit, it sucks to have anything stiffled.