I fully understand the religious thing. I also understand the feelings thing. I wouldn't sit down to talk about feelings, but it would be more of a "what's up? why didn't you come" type convo. Just try to get details to clear up why things didn't work out. Shockingly, though, the forgiveness thing is in-part a choice to live and let live. Shutting everyone out of your life for trivial and one-time offenses is no way to live. You have to give everyone a second chance at least once, and you'll find better things coming to you.
Try it, just once, especially with friends. I give my friends and family more leniency than other people, but it is the basis of a relationship that there is some slack in what there is. This could be something just blown out of proportion, and I think you'd be surprised at his response.
I don't sit down and pour my heart out, but I typically can gauge people's response when they address me. If a friend called me and was asking why I didn't show, etc. I would get the vibe that the occasion was more important than I perceived. Who knows, maybe the other guy's situation happened.
If you really wanted to look at the severity of the situation within the confides of losing all reasoning: would you react the same if he was in the ER because of something, but still failed to show. He didn't hold true to his word, but if he didn't tell you that, but told you something came up; would it still be as "grudge" oriented as it is now? I say this just to realize that sometimes people have to break their word for reasons they can't always explain to the other party, and that outward appearances are not always the underlying reality.
No cause there would be no way for him to come if he was in the ER and I'm his best friend his parents would call me. If he told me something came up, and it was a valid reason, I would still be hurt but probably not as bad. My friend called him to find out what happen, his reason was he was tired after spending time with the girl he ditch me for....