This is a fear I think a lot of people have when it comes to learning a language. They fear investing all that time and energy learning a language and then having it go to waste. Or they fear if they learn a language, they have to spend a ton of time and energy maintaining it.
I’m here to alleviate those fears.
In my experience with learning (and forgetting) languages, what you’re left with depends upon how far you got in the first place. The good news is that generally, no, you don’t lose a language if you stop using it. If you take an extended break from a language, expect your ability to take one step back. If you were at an advanced level before your break, expect to be now able to speak fluently but with a lot of rust. If you were at a B2 level before, maybe you can now operate a B1 level.
The good news if you can very quickly get back to your previous level with a few weeks of consuming material in your target language. I’ve stopped learning and practicing with a language many times. There are many times, where I would take a break from a language either because I was happy with my level or I found another language to work on. Then later when I wanted to pick it up again, I would start practicing again. I actually find it interesting studying the second time around as I’m able to notice and pay attention to things I wasn’t able to the first time.
The only danger you have of really losing your language ability is if you didn’t really get to much of a level in the first place and the language is quite different from English. This was my experience with Romanian. I spent a few months learning trying to win a bet and then completely dropped it until years later. When I started practicing it again, I found I could recall practically nothing. That said, when I started practicing again things started coming back and it was much easier and faster learning it the second time.
So, my advice to you would be don’t worry about taking a break from a language and losing it. If you get to a sufficient level, say early intermediate or B1, your language ability only goes into hibernation and can be easily revived by watching videos and reading articles in the language.