Remind someone about their rough past? ?

My best friend has had a horrible past and has gone through just about everything you can name. I'm not going to explain it but there's a reason why people who know his story say he has unbelievable strength and they're shocked beyond belief. His past would often come back and haunt him; only I can bring him happiness because we are together, and I'm really surprised I could make him that happy. Last week, he got in a fight and hit his head, and lost all his memory. Just recently he's gotten back the ability to do most things and some good memories with me and his friends, but I've had to explain to him about something horrific someone did to him because it's impacted his life in many ways, and he had been wondering why things the way they were. There's much more to it and he has the right to know about the horrible things that happened before... But should I tell him? He is planning to move where I am and completely start anew. Would it help for him to know how bad his past was if he is really curious? I don't want to have to hide anything from him, but I don't want knowledge to haunt him again if he has a new chance to start anew. What do you think I should do?