Very interesting question! I always thought that it was pretty much as stated. Stevie was moving out and leaving Lindsey, so that is the "packing up" part. Packing up her stuff to leave their home together. As for the "shacking up's all you want to do" part, I believe that Lindsey felt he was taking the relationship more seriously than Stevie. Lindsey wanted more from the relationship, maybe something more permanent like marriage, engagement,etc., and Stevie was content to leave things as they were: them living together, aka shacking up.
