If I couldn't delete it, I would comment on the fic adressing "Alex". That way I could at least know people who read the reviews could get my side, because otherwise it would drive me nuts too.

Also, that commented is an idiot for reading a fic that they're predisposed to dislike and then blaming you for it. I mean, no matter what, you're going to have to break up S/U to make the story work, so getting irritated about that makes no sense. I mean yeah, maybe you could have done it differently, but your version of them gradually breaking up is far more realistic than how most people write it!