How does Finn know what a boyfriend is when he asks Rey whether she has one? Kylux. Every Stormtrooper and officer in the First Order knows (and gossips) about the romance of this train wreck of an evil power couple. Either they used to be boyfriends years before TFA and then became bitter exes or they are dating while they (pretend to or actually) hate each other.

Once Finn joins the Resistance and starts to date someone (Poe, Rey, both of them, someone else) he quickly realizes that here people think about dating and romance quite differently than his previous commanders (though I'd love it if there were some similarities as well!).