Tiggy, sound slike yours and mine are alike. As mine are chalk and cheese, too. One is academically brilliant, but socially inept, one is sporty and had lots of friends, but no where as near academically inclined!!!
The "sporty, social" one wants to separate, but the "loner, student" is devestasted at losing her only friend. The teachers recommended they stay together as the benefits to one outweighed the loss to the other!