I see what you're saying about all other factors being right. I'm relating my experience to add to the data you're collecting (
): in my case the relationship lasted a handful of months. I also think most other important factors were just about right, but not all. There was nothing wrong per se, at least not anything i could accurately put my finger on and isolate to work on, just a certain inability to properly, fully, understand where the other person was coming from and inability to establish proper trust and re-assure one-another.
Oh, also, a dual came along (the other person's dual, I mean)...