I went to French high school and English was the only second language offered. But honestly, 99% of us were already fluently bilingual by that point, so the English classes were advanced and were not about learning the language, but things like literature, history, science, etc. Basically, a regular high school class but in English.
At uni, I took German for a few years, and then kept up the language on my own while commuting. Eventually - and by pure chance - I met my future ex wife who is German. We spoke a lot of German at home. Even now that we're no longer together, I read German books, watch German shows (usually in German with German subtitles to reinforce the language).
Like others have said, if you just learn the mechanics of language, you'll forget it soon enough. You actually have to incorporate it in your life if you want to develop. In our public schools here, kids in the English system have 12 years of French, and by the end, less than 3% are bilingual. It's because they just don't use it outside of the classroom.