Blaine and Kurt's families have been friends since before the two were born, and Blaine is two years older. The two have been best friends since forever, Blaine being a big brother at first to Kurt but things changed. I think they started dating in high school, and went long distance when Kurt went to college in New York. I remember in the end we find out that Blaine became a firefighter. Ringing any bells?
Also, if you have any other fic recs of this type, they're welcome!