[ cardinal number] years (living as a couple
The German phrase 'vier Jahre' translates to 'four years' in English. It is used to express a duration of time, specifically four years. In the context of living as a couple, 'vier Jahre' would be used to indicate that the couple has been together for four years.
I lived in Berlin for four years.
This sentence uses 'vier Jahre' to express a duration of time in which a certain action (living in Berlin) took place.
It takes four years to get a degree.
This sentence uses 'vier Jahre' to convey a general time required to complete a certain task or action (in this case, earning a degree).
She studied piano for four years.
In this sentence, 'vier Jahre' is used to describe the span of time during which someone was learning to play piano. The term 'lang' after 'Jahre' is often used to indicate a period of time characterized by a certain activity.