Well, in short, IMHO it's never about orientation of a relationship, it's about consensus, honesty, well-communicate through between parties
My wife and I have been together for 11 years now and still counting, I made mistakes in the past, cheatings, affairs, and nearly ruined our marriage at one point when I met someone in our neighbourhood. Lucky me the lady halted when she knew I have a wife who loves me so much (what's worse, she's my colleague till today, a guilt that reminds me whenver)
4 years ago, I spoke to my wife about divorce, because we are so different, she lives by the day, but I'm a planner, she's very self-preservation person, I am extremely sexual. She was so hurt to a point she lost herself, accidentally threw house key while housekeeping, crying at the corner while I was not noticing (but I did, because I love her so much, I noticed every details about her)
I knew I could not divorce her, because she loved me and I loved her too, it was about our consensus, it was 100% my fault things happened behind her back, and it was 100% my responsibility. Hence instead of continual hinting divorce as a solution to her, I took a step back to remedy my mistakes, I promised her to be completely honest to her (and all the details if she is ready to hear out), however she needs to open her palm, let me go meet other people, and we as long as I am allow to, she is allows too, we are equal. And our consensus till date, we never meet people in our city(Singapore), and we never meet people who share same culture/language
3 years since then, we are extremely satisfied couple, she loves me even more now, seeing how other ladies treasure me, and I always appreciate her as a person who allows me to travel and meet ladies abroad, I have so many beautiful memories since then learn how to respect and love her better
We are Singaporean couple, and since this year I have an English girlfriend, she enjoys connections with Italians (she's a big fan of Italian cuisines). By definition I guess we are polygamous, though we never meet people as a couple