What a frustrating experience you must have had!
Email communication so easily turns to miscommunication, doesn't it? I write as a hobby and despite all my practice still find I can't avoid misunderstandings.
I remember that on our third or fourth date my GF asked if I might feel able to meet her husband. It seems to me that such a meeting is a very positive step that should be taken early on. I hesitate to be dogmatic, especially since I'm a newbie too, but in my limited experience it has been immensely helpful to know and be accepted by my GF's primary partner. Besides, he cooked us a great dinner...
That meeting might be something you gently insist on next time the merry-go-round turns. The dinner at least!
I do use the terms primary and secondary, and I use them with intent. Part of my goal as a secondary
is to make sure that I do what I can to nurture the primary
relationship. First, I know that my darling's happiness centers around this beautiful marriage, and I very much want to care for and enhance her happiness. Second, it is the nature of the relationship between her husband and herself which makes it possible for me to be with her at all, so caring for that relationship is important. And third, I like and admire her husband and don't want to cause him distress.
So I use the label secondary
as a kind of shorthand for a set of constructive attitudes and behaviors. It is not in the sense of "second-class" at all.
Your mileage may vary. If the word feels bad then define something else. But it seems useful to think about your role in a relationship and how it can work to support both the other people, or all the other people. You can't always control your feelings but you can attempt to guide yourself toward mindfulness.
I'm also aware that not all relationships are as stable and as psychologically open as my GF's marriage. It was -- and is! -- delightful to be involved with people who are so centered and conscious. That's not always the case. Your mileage may indeed vary.