Although I agree this may not be the best analogy, I'm a bit amused by your take on it. On the one hand, you suggest there is a victim if you back out on your prom date; however, it really isn't a big deal because it's just one night. While I agree it is probably harder on the girl than, say, the coaching staff and other players you made a promise to, it's only McDonald who is impacted for the next 3-5 years? Remember, McDonald helped talk Nelson and recruits into coming to MN after he made a commitment. Furthermore, I guess this implies we shouldn't worry a whole lot about the girl because (with some good counseling) she'll get over after a month or two.
I understand kids have trouble making up their minds but I'm with those on this board that see this as a potential red flag. If a kid thinks it's O.K. to back out on a commitment of any kind (and this kid has done it twice now), they're probably more likely to repeat it in the future. Again, he may have some compelling reasons for what he has done and, if so, fine. I just hope Coach Kill never trades personal integrity for star power at the risk of poisoning the water.