Como usted está con nosotros más de dos años. Because you have been with us for more than 2 years,
Como vs Porque
August 15, 2014
August 16, 2014
This tracks pretty closely with English: "because" vs. "as". I think a better translation (and better English, quite frankly) of the above sentence would be: "As you have been with us for more than 2 years..."