I don't know. I honestly don't think so, but... I love him so much. We've been together for two years and he supported me when I came out as NB, so I'm really confused about what to do here.
I think you should think about both peoples happiness and comfort. Are you comfortable with him being polyamorous? Would you feel upset if he had other partners? And what about him? Talk to him and tell him how you feel. It's better to discuss this with your partners than to ignore it and make one of you uncomfortable.