Keeping your first language alive after a move takes effort: shows, calls home, counting in it under your breath.

Languages fade through disuse, not through distance. Without daily contact the vocabulary goes first, then the speed, then the willingness to speak at all in front of people who are fluent, and the loss is slow enough that you only notice it years in. Twenty minutes of real contact does more than an hour of study.

So build a few fixed points: one call home a week in nothing but that language, a show you actually like, the numbers counted under your breath while you walk. Text your cousins in it. Keep it in your mouth rather than in your notes.