Game of Thrones has been giving us hard-hitting reunions all season long, but the Season 7 finale delivered on ones we'd been waiting for for years. Jon Snow, Daenerys Targaryen, the Lannisters, the Cleganes, Brienne of Tarth, and all their respective advisors finally converged in the Dragonpit for the great negotiation regarding the War to Come. It was successful, largely thanks to Tyrion, who has been greasing everyone's wheels all along. Cersei and Tyrion's reunion on Game of Thrones was a powerful scene with Emmy-worthy performances from both Lena Headey and Peter Dinklage.
Tyrion insisted on going to talk to Cersei (promising Jon Snow that he'd definitely get murdered if he tried to do the honors), forcing the others to stand down when she refused to align herself with them against the White Walkers. She would only agree to a truce if Jon Snow promised not to take sides later, when the time would come for Cersei and Dany to duke it out for the Iron Throne. Jon couldn't agree because he had already pledged fealty to Daenerys. (Curse that Stark honor!) So Cersei walked away from the negotiating table (negotiating pit?), refusing to pledge Lannister armies to fight The Night King.
Tyrion bravely met with her sans protection while The Mountain loomed nearby. Cersei unleashed years' worth of fury upon her little brother, shutting him down every time he tried to offer condolences for her dead children (even though he obviously loved Myrcella and Tommen). Cersei was determined to blame Tyrion for ripping their family apart, while Tyrion insisted that he was just trying to survive. Eventually, Tyrion dared her just to order him dead already. It was his "fault," after all, that Cersei was motherless, fatherless, and now childless. And for one harrowing moment, The Mountain started to draw his sword. But in the end, Cersei couldn't do it, begrudgingly letting her little brother live.
Getting to the heart of the matter, Tyrion wondered why Cersei was still so hellbent on clutching to her crown when she had proof of what the Army of the Dead is capable of. She admitted that when she saw the wight Jon et al had presented her with, she didn't think about saving the world at all. "All I could think about was keeping those gnashing teeth away from the ones who matter most, away from my family," she confessed. Tyrion immediately spotted it: "You're pregnant," he realized.
And so ended their family reunion. He likely knows Cersei is more dangerous than ever now that she has another child to viciously guard. But with the Army of the Dead past The Wall, Cersei's self-preservation tactics won't get her very far.