That was really nice.
I liked Yukino's comment about "still". When you use the word 'still', there's an implication that the status of the subject could change (eg. the clothes are still wet (but could be dry), the milk is still good (but could be off), the show is still running (but could have ended) etc.) - but when Yukino dismisses "still" from Nobara's comment, there's the implication that there is no alternative status. Nobara is and always will be her number one.
I liked that. It works in English at least - not sure if that's how it literally went down in Japanese.
Also, a pretty bold claim considering modern divorce rates and relationship failure rates, but the sentiment is very sweet.