I don’t think it’s unhealthy to stop holding a grudge, but I do think it’s unwise to let someone back into your life after they have mistreated you to the level that you’ve decided to cut them off in the first place. My former best friend stole $400 from my mother through a con, most likely to buy drugs. I am no longer angry at him about it, but he will no longer have a place in my life because, firstly, people who con old ladies are not people I wish to associate with and, secondly, he could do something similar or worse.
So I don’t dwell on him, I don’t want to find him and slap him or yell at him, I just don’t want to be in touch with him anymore. I don’t hold a grudge, I just don’t want him in my life.