It says to me that that person had a deep effect on you and that you miss him or her. Also that there might be some unfinished business that needs to be attended to and that you are trying to work out a solution via your flashbacks. Just a guess. There can be many reasons for flashbacks.
It just means that you miss them very much. This is very normal, especially if you cant see them anymore because minds tend to exagurate, and make you feel worse.