Repeated renewals of a "visa to study German"

I'm really here to see my German honey, but need an official reason, so I enrolled in a German course, and got a visa for a year. How often can I get away with this. I'd like to do it for two more years, until my sweetie quits work, and we can move to Thailand. BTW, I plan on taking the course, and am happy to be learning German. No, really! PS. I've got no other excuse: I'm retired and we don't want to get married.

I think there is a 2 years limit. A friend of mine is facing a problem right now because it took him 2.5 years to manage to get in to the Uni and now the A.B. does not want to renew his visa.