This one is hard. My primary-ish relationship is with a man who also has a live-in girlfriend who's been part of his life for years before me. His family and the people he works with know her as his partner. He doesn't want to be out as poly with family or at work, so I'm secret from them.
That's the extent of the secret, though. Our friends know. My family and her family know. But still, I worry that if something happens to him, if he were in the hospital or something, I'd be out of the loop.
I respect his decision to be closeted. People at my job know nothing of my personal life, so I have my own closet there. It does hurt, just a little, to run into his coworker at the store and be introduced as his friend.
Social recognition is something that we value for our relationships. It's normal. And while a lot of poly people are closeted in some ways, not all of us are. I have a friend, who has two partners, and everyone knows (her kids, her work, her family, the PTA, everybody). I'm envious sometimes of her courage.
You do get to decide for yourself what level of secrecy is okay with you, and what makes you feel too insignificant. Don't presume that you deserve to be kept hidden away. If it makes you feel bad, you should pay attention to those feelings, and figure out how big they really are.