Can a person change his/her ways?

My fiance and I are on a break for a month. He has caused me much pain and heartache. He was selfish, verbally abusive and manipulative. He used my feelings for him to bend me to his will. (Example;I'm leaving you if you don't stop arguing/bringing up issues with me) It was my idea to take the break because I was at my wits' end. He realises how much he has hurt me, but the question is, is it possible that he could change his behaviour? Has anyone had experience of this?