I think this point about being discreet is huge. My husband and have been open/poly for a decade (ie from the start). We don’t keep it a secret by any means, but most people I know have no idea — it just doesn’t come up in conversation very often.
We had a very bizarre situation recently where one of my closest friends saw my husband holding hands with his girlfriend at the beach. She texted me frantically, saying she just wants to support me and is here if I need her and she hoped she was doing the right thing by telling me. It was pretty trippy to tell this friend who is close enough to know super specific details about very private parts of my life “oh cool thanks but it’s chill.”
Non-monogamy isn’t for everyone, but it’s for a lot more people than you might think.