I think when you sincerely apologized you did all anyone can. We, at least most of us has had a time when we regret writing or saying something about another. One could retract the whole statement but once the other person knows about it there is not much you can change. The other person has to be willing to practice forgiveness. At some point they may do this but probably not before the hurt lessens for them. I don't necessarily believe that time heal all wounds, it depends on the circumstance. Pray for the person and let God work on their heart. I know of nothing more you can do outside of show that person love, sometimes that will break down the walls.
