For me, it means that the woman wanted to move on and do more with her life. He didn't want to let her to go, so they fought, until he got so mad that he just didn't care what happened. After that, he replays the fight and the relationship over and over again in his head, trying to figure out what went wrong and why. He regrets the bad things he said and for not figuring things out properly. He will never forget her because he truley loved her, and because of that, he knows it was the right thing to do by letting her go so she could be happy.