Would you rather have a supportive friend there with you, or would you rather have your dickhead boyfriend there who is really bitter about this and blames you for something that's not entirely your fault?
Also, I think you should think about this decision more because it sounds like you might be doing it mostly for him. I know it's a really difficult decision to make, but seriously, it only matters what YOU want to do about it. His opinion of what you should do should have no bearing on what you end up choosing. I think you should reschedule your appointment for a week or two from now (just make sure you won't be outside of the allowable time frame) and spend that time completely away from him and decide what you want to do. What would your decision be if he had totally abandoned you and disappeared when you first told him? I think that's an important question to ask yourself.
If you are only doing this to save your relationship and make him more comfortable, I think you might regret it later. With the way it's going now, it seems likely that your relationship won't survive this. It shouldn't survive this anyway, not because of anything you did, but because he acted like a selfish brat and treated you badly at a time when you really needed his support and kindness. For that alone, you'll probably have some resentment toward him, and rightly so.
I wouldn't want to be in your shoes. Good luck.