It's after Haruka and Michiru officially join them that Usagi starts noticing it, and once she does she can't block it out no matter how hard she tries.

Haruka spent her entire life trying to outrun her destiny. Ami turned down an opportunity to study in Germany. Minako hasn't put out that demo tape she keeps talking about. Naru's never really recovered from the loss of Nephrite. So many beautiful dreams deferred or outright shattered.

It's why she encourages Mamoru to go and study abroad when his opportunity comes. Usagi doesn't want to ruin any more lives.