My gf, Gia, and her husband, Eric, have been together for 15 years, married for 6, and open, to varying degrees, throughout most of that time. They both dated the same girl once, which ended poorly and nearly broke up their marriage because of trust violations on Eric's part related to the whole thing. They closed up for a while, worked through it, came out stronger than before, re-opened, and Gia and I started dating not long after. We've been together for more than three years. Eric's not dating anyone seriously, but has had a few fwb's during that time. My bf, Davis, and I have been involved on and off for ten years, with this most recent try having been for the last year and a half. He's not interested in dating others himself, but is ok with Gia. So, that's our story, timeline-wise.
I will say one thing -- the veto power concept may be feasible now, but, down the line, may be less so. When you've given your heart to someone, and time and intimacy have strengthened that bond, made it one of both trust and passion... when your partner has become not just a part of your life but a part of your heart and mind, when the holidays are barely over and you're scheming about next year's presents for them... how can you just drop them because someone else gets cold feet? If Eric suddenly told Gia to break up with me, I think we'd break up... if nothing else, because I couldn't stand the idea of sticking around if he wasn't ok with it. But I think it's fair to assume she'd be heartbroken, and that it would put a significant strain on their marriage.
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.