Examining what Lukeprog wrote...

Before long, Alice was always pushing me to spend more time with her, and I was always pushing to spend more time studying psychology. By then I knew I couldn't give her what she wanted: marriage.

So I broke up with Alice over a long conversation that included an hour-long primer on evolutionary psychology in which I explained how natural selection had built me to be attracted to certain features that she lacked. I thought she would appreciate this because she had previously expressed admiration for detailed honesty.....

...his stated reason doesn't appear to match the paragraph that preceded it all (I realize that we are probably gettting a very condensed version of the conversation, but hopefully it didn't elide something this important).

Were I in the lady's position, I'd wonder why I only became physically unsuitable after I started seeking a legally recognized commitment. Unless the feature Lukeprog found unattractive was "wants committed pair-bonding," the explanation does not appear to fit the circumstances at all. This doesn't seem like a case of someone unable to deal with "radical honesty;" it seems like a case of someone being pissed off at what comes across as dishonesty.