Poe's secondary gender fails to present until a very late time in his adolescence but nobody seems overly concerned about this because everyone just assumes he will present as an omega. All the signs are there: he is short and pretty, kind-natured, charming, loyal – and if nothing else those childbearing hips of his are a dead giveaway. In fact Dameron family has been receiving offers of bonding and marriage proposals from influential alphas for years because promising, young omegas like Poe are considered a rare prize anywhere in the world. So, naturally, when Poe finally presents as an actual alpha the news becomes a fad of galactic proportions.

…And Ben Solo goes completely berserk.

The thing is, ever since Ben presented as an alpha at a very early age he was desperately hoping that his best (and only) friend's secondary gender would turn out compatible to his own so they could form a full, life-long bond (and even Poe himself didn't seem too averse to the idea) - he always felt certain that he could never love anyone the way he loved Poe. But now all his hopes have been shattered and, unfortunately for everyone, this was exactly the push Ben needed to finally fall under the influence of Supreme Leader Snoke and cross over to the dark side…

Bonus:
- relationships between alphas are unheard of because their natural instincts to claim an omega mate usually override all other desires, but they're not actually impossible
- when Ben/Kylo Ren captures Poe on Jakku they are both still unattached