Wanting to be mono is fine, but this argument for it always kinda bugs me. I mean, if your partner had no other friends and family you'd be the most significant to them you could possibly be! But wait, that's messed up. My partners are significant to me and me to them not because they have no other outlets or options, but because of the strength of our connection when we're together.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.