there is a long pause after lexa stands up, she gazes into your eyes with so much love and care, after a while she says

„good night ambassador.“

even if your motive is more political and not personal, it still helped save lexa’s life. after you told lexa about roan saying that he wouldn’t kill nia but she could..he wouldn’t be against it. this was one thing lexa was thanking you for. she was thanking you for finding out about ontari and approaching roan about being king. If lexa won her duel against roan - killing him - nia would still be alive and probably try to kill and replace her with ontari which would be a disaster.

also back to the „good night ambassador“ which lexa said you answer with

„Goodnight, commander“

in trigedasling and lexa said „good night commander“ in english. this is a respectful gesture, and at the same time a caring gesture from both of you.