I don't know. I don't relate to doorslamming as a way of life. From what I've read here, many people have said they did it more when they were younger. There are very few people that I would. The very few (2?) times that I ever did it were in response to realizing that the person had been lying for a very long time. I am pretty forgiving when I can see where the person is coming from and can stand in their shoes. That kind of deception though (especially when it affects other people than myself) indicates something about character and that the person simply isn't the kind that I want to have for a close, close friend (I don't doorslam acquaintance friends. If they're not for me, I just sort of let the relationship to them become more and more periodic).
I suppose if there was evidence (over a period of time) that the person had changed and if they acknowledged what happened, why they think it happened, how it affected those around them and why it will not happen in the future and they've regained my trust, I may rethink things.