What was the whole point of Preston writing a letter for Amanda in the first place?
I'm sure that this sounds obvious, but what was keeping him from actually talking to her in the first place? I mean, it isn't like Amanda was harder to get in personal contact with given that they went to the same high school for four years. Thus, Preston had plenty of time to reach out to her without attempt to win her over with a stale and sappy love letter.
And Denise did have a point that Preston comes across looking like an opportunist by giving her his letter right after she and Mike broke up. Also, Preston when you really think of it, comes across as looking a bit shallow, giving that he is writing about the Amanda that he personally imagined or dreamed about.