Lotor is (reluctantly) accepted by Team Voltron. There’s a lot of animosity between them, but one-by-one Lotor suddenly begins to treat each member nicely. Team Voltron can’t figure out what’s going on until they finallly get together and Coran sheds light onto the situation. It turns out that on different occasions they each, quite accidentally, proposed to Lotor. They just didn’t know it (because Galra culture is so different from Earth’s).
Hunk made Lotor a meal and included a baked dessert - a traditional (and quite serious) symbol of love. Lance gave him a high-five. That’s right. That’s all it took. It was one of those high fives with an “explosion” after too. Very by-the-book as far as Galra declarations of love go. Keith flipped him off, another Galra gesture of proposal. Pidge challenged him to a game of chess (a show of intellect and strategy - a common precursor to proposal) and beat him, shaking his hand (or as he saw it, finalizing the engagement) after. When he moved to give her a kiss (to show his acceptance) Shiro got protective and slapped him. A left-handed slap to the right cheek is the Galra equivalent of getting down on one knee, granted both members are of the same sex. And Allura offered him a flower she thought symbolized peace (she remembered incorrectly and should’ve really consulted a reference book).
The only one they couldn’t figure out was Matt. Clearly, Lotor treated Matt like the others, but he denied doing any of the traditional Galra proposals that Coran told them about. Finally, Mart suggested with a grin, that maybe Lotor got the idea that he had proposed when he said “Hey we should get married.”