It's a conjugation of the verb "acabar" (to finish) in the first-person plural form.
Here's how it's used in different contexts:
* We finish the work: "Nos acabamos el trabajo."
* We end the party: "Nos acabamos la fiesta."
* We finish eating: "Nos acabamos la comida."
* We end up together: "Nos acabamos juntos." (This could also mean "We end up together, but not necessarily in a romantic way.")
The exact meaning of "nos acabamos" can vary depending on the context. It's important to consider the surrounding words and phrases to understand the intended meaning.