Thanks for your reply Ciel. I was thinking more along the lines of everything non-sexual. (Sexually for me there's no compromise in that sense. If anywhere along the chain of partners there's any risk, I don't get involved.)
But, I was thinking more along the lines of the stuff that goes along with it. What it's like to be witness to a rocky relationship, for example, between your partner and their partner. What do you do if they are being unfair/mean/dishonest/? with their other partner, but wonderful with you? How much does their behaviour with someone else, which is behaviour you wouldn't tolerate for yourself, weigh in?
My heart is too big to fit into one person.