It's a bit hard for me to picture that kind of thing, since I usually start with falling in love with someone, at which point I'd tell my partners before doing anything else.
But I see what you mean. I think it might also depend on each relationship and the way it evolves.
Me: 31F, straight
Seamus: My husband, 32M, straight
Dragon: My boyfriend, 29M, pansexual, married to Fox
Fox: My boyfriend, 29M, homoflexible, married to Dragon