Resultados posibles:
estabas uniendo
-you were joining
Imperfecto progresivo para el sujeto del verbo unir.
estabas uniendo
-you were joining
Imperfecto progresivo para el sujeto vos del verbo unir.

unir

No sabía que te estabas uniendo a nosotros.
I didn't know you were joining us.
Palabra del día
la leña