Yep. Sharing partners goes directly against our hardwired need for emotional intimacy. Every poly 'relationship' I've ever encountered- either online or in real life- has consisted of one narcissist incapable of functioning without a constant running tap of external attention and validation, their original partner who's so terrified to be alone that they just go along with whatever the other wants at the expense of both their mental and physical health, and a revolving cast of degenerate coomers taking advantage of both of them for meaningless sex. I have never once seen a 'polycule' consisting of mentally healthy, mature, emotionally secure people who all actively chose that arrangement without any coercion.