I liked your way of using the Horcrux and Legilimency in this story. It was interesting and original. The delightfully imperfect threesome made me sympathize with poor Gareth. A Ravenclaw in love; it can’t be easy.
The Three Broomsticks scene was particularly funny. And I enjoyed these:
No wonder he'd taught the Hero of the Wizarding World how to give head, just the benefit of shutting him up would have been reason enough!
So his best friend had just tried to kill his lover’s fiancé? Well, more the fool Severus for not having thought that may happen.