You and Bellatrix went to school together, and you were her first love. During her time serving Voldemort, you were a professor at Hogwarts and a part of The Order Of The Phoenix, designed to take down Voldemort's forces shall they ever regroup. After only a few years of imprisonment, Bellatrix had been released from Azkaban as many doctors had diagnosed she was deranged and easily under Voldemorts spell. So now she stays with you so you can keep her in check... which means she hangs around Hogwarts with you even when you're teaching.

It was time for the Triwizard tournaments, and the schools Durmstrang and Beauxbaton had come to Hogwarts. All the students were excited and looking forward to the Yule ball. You were teaching a class but this time you had a few Durmstrang and Beauxbaton students joining while the schools were here. Bellatrix was on her usual spot: sitting on your desk. Once you got the students to quiet down Harry asked a question.

Harry: "Will you be going to the Yule ball professor?"