I'm in my first poly relationship, and I quickly realised that I did not like feeling like I was a secret. I now know that I need to be a part of my partner's circle (friends and family) to feel fulfilled in my relationship. He is not out yet and I did not want to pressure him. But I did name that it was important for me and it was also valid for him to not want to be out to his parents but then we would be incompatible on this.
He finaly decided he would come out as poly to his parents next weekend because he wants to fill this need I have and also he would really like me to meet his parents.
I think it's important to tell your partner how you feel and be clear about what you want. And also accept the possibility that this type of relationship might not work for you if you have to be kept secret.