The day he found his wife in bed with his best friend, he felt his life crash down around him. How could they betray him like that? He had vowed then that he would never give either of them a second chance. The days that followed were hard for Derek. He had to make huge, life-changing decisions quickly, something he should have been good at as a brain surgeon. He shut himself out from the world, from his friends & family, to concentrate on the many questions which filled his mind. His phone was constantly ringing: calls from his wife & best friends, wanting forgiveness of at least a confrontation. Usually, he'd want to talk it through, find & kill the problems which lead to the disaster, but this was different. This disaster wasn't something he could fix with a scalpel. As much as he wanted to know the reasons, he couldn't face them. He needed to get away. It was then that he remembered the call he had received just two weeks ago from Richard Webber. Webber was the Chief of Surgery at Seattle Grace Hospital. He had asked if Derek & Addison wanted to work with him at his hospital. They had turned him down, but Derek had a feeling it wouldn't be too late to change his mind.
It was settled by the next morning. He would leave New York whenever he was ready, but he was more than ready. It only took him a few hours to pack, he had nowhere to stay in Seattle so he couldn't take much, & he found some pleasure in leaving behind photographs of him, Addison & Mark. He would send her the keys, she could pick up the pieces he left behind.
He didn't leave a note, nothing to say where he was going. He knew Addison would remember how keen on Seattle Derek had seemed & realise that was where he had gone. But he was too hurt to care. She could come to Seattle, pour her heart out, beg for forgiveness, whatever she wanted. But he wouldn't cave. He promised himself that.
He arrived at Seattle Grace Hospital, a new doctor with nothing on his conscience. Nobody knew his past, his, pain, or anything about him. That was probably the biggest factor that attracted Derek. He had told Dr.Webber that he & Addison were over, he didn't want to be reminded of her. He didn't go into details, just that she was in his past now. He didn't want the sympathy he would get, & besides, he doubted he could tell anyone without either breaking down or breaking something.
So he started a fresh new life in Seattle. Nobody, except Webber, knew he was ever married. He was the mysterious new doctor, he loved that, he thrived on it.
He revelled in the attention her got. Took in the praise from fellow doctors & felt he settled in well. He liked Seattle, & for the first time in his life, he gave something a second chance: love.