Lexa normally talks to Clarke in English because its the language Clarke understands the best. But ever since she discovered Clarke's drawing of her, she starts telling Clarke good-bye in Trisgedaslang. Even though the blonde is starting to pick up on the Grounder language, she'd never heard that particular phrase before. When asked about it, Lexa simply explains that it's a farewell reserved only for those that have gained their full trust and unwavering loyalty and in grounder society, these types of relationships are very rare, which is why Clarke has never come across it before.
A few weeks pass with the two continuing their late night talks, both political and personal. When Lexa says goodbye to Clarke one night, the blonde repeats the phrase back to her, causing a heartfelt smile from Lexa.
Every night from here on out, the two exchange the now familiar farewell with Lexa always smiling and her eyes shining. Clarke has completely forgiven Lexa for Mount Weather and has faith that their alliance is different this time because Lexa's reactions to her good-byes are so pure and sincere.
Octavia stops by Clarke's room the night before the grounder blockade of Skaikru is enacted to discuss their departure the next morning. Just as she's about to knock on the door, she hears the two say their Trigedasleng good bye's that have now become second nature to both. Lexa opens the door and almost jumps when she sees Octavia on the other side but she quickly recomposes herself and walks away with the presence and confidence of The Commander.
After Octavia and Clarke plan their route and plan of action once they return to Arcadia, Octavia turns to leave the room.
"See you tomorrow," Octavia casually mutters.
At this point, Clarke knows Octavia is still quite upset with her allowing Lexa to enact the blockade, so to show Octavia that she is still loyal to her and the rest of her people, she decides to use the Trigedasleng farewell Lexa taught her.
"Ai hod yu in," Clarke replies, as she'd done many times with Lexa.
Octavia stops in her tracks just as she's about to open the door.
"… You do know what that means, right?" she asks.
Clarke sighs in frustration. "Look, I know you're still pissed off at this whole blockade thing, but I just wanted you to know that I'm still just trying to do what's best for our people." Clarke starts pacing, upset that Octavia doesn't seem to want to accept her peace offering.
A few seconds pass with the two in silence. Octavia quietly opens the door and looks back at Clarke.
"It means 'I love you'," she comments, closing the door on a speechless Clarke.