I've only read the first couple of pages of this thread. I hope I may throw in a couple of suggestions.
If you don't care for the terms primary and secondary, perhaps one or more of these may fit better.
For those who are married: husband, wife.
For lovers to whom you are not married: boyfriend, girlfriend, lover, sweetheart, benefriend (for FWB's).
In my tribe, most of us use husband, wife, bf and gf, but one of my bf's lovers doesn't like those terms. She just refers to each of us by our names.