Why would you cry “over” spilled milk? For one thing, unless you’re a clumsy dairy maid, it’s unlikely that you’re crying because you’ve actually spilled milk. And, even if you are, it’s entirely possible that you spilled it because you slipped and fell; in which case you’re crying alongside, or even possibly under, spilled milk. When it comes to the spilled milk, however, the problem isn’t so much the literal versus the figurative: the problem is all about the preposition. Either way, you’re almost certainly crying ABOUT spilled milk.