Originally Posted by psylockolussus
Magneto didn't say second in command but he said he needed someone to fill a gap in his life. He and professor x just parted way and it looked like he was looking for a new partner or a 2nd in command kinda like Professor X. And he offered Emma Frost to fill that gap for him. And judging by Emma's reaction, it felt like she went along with him.
He has Mystique to fill the gap.