parshanut torah comment - Why did Ya'akov work for Lavan for so long?

I'm having a bit of trouble understanding Or Hachaim's explanation on Breishit 29:18. Usually Jewish slaves work for only 6 years. Yet, Ya'akov offers to work for Lavan for 7 years as payment for marrying Rachel. Ohr Hachaim says that there is a "secret" behind the number 7. Despite that, esp. if Ya'akov had already suspected that Lavan was not trustworthy, why did he offer his work for so many years? (I may be missing something in Ohr Hachaim's explanation that would answer this.)