I don't think we're actually saying different things, lol. It's not that he wouldn't react that way, or that it was out of character for him to leave. Just that, from the characters' perspective, he shouldn't have, because it was the wrong thing for Buffy at that point. In other words, just because he was acting in character, that doesn't get him off the hook for ignoring the problem, any more than, say, Willow should be let off the hook for erasing Tara's memory because it's in character for her to abuse magic.