So-Called Mistake #1: You Drop the Love Bomb
Oh, God...you had the weird dark beer (with the hugely high yet unmarked alcohol content), or the two of you spent the night together for the first time (and it not only wasn't awkward, it was almost spiritual), or you witnessed him save the life of a puppy by diving into the street just before a speeding car barreled by, or—and this is by far the best case scenario—you looked across the table at him just as his eggs fell off his fork and onto his lap and felt as if this particular guy might just be the goofiest, funniest, most-perfect-man-for-you-ever. At which point you thought, "Why not just say it? I'm a grown-up," and the words "I love you" came out of your mouth.
On date three.
Or some other timeframe officially known as "way, way too early."
The odds are, the guy is not going to say it back. (This is a good thing; you two really don't know each other yet.) So...you're going to have sit through one of the longest silences in your life, one in which you will be able to hear the sound of cells dividing and molecules moving through space. He may eventually stammer, "Thanks?" or pretend it never happened. But the gulp-inducing truth is out. If he flees in terror, there is an upside: You will not have to waste a lot of time with somebody who is afraid of commitment. That kind of individual will be out of there, but he was always out of there, and you just saved yourself the heartache of trying to convince him otherwise. For the undecided but interested guy, the one who likes you right now but is a bit overwhelmed at your revelation, things might be a little weird. But you have set an admirable precedent for the relationship, one that is exceptionally helpful on month three or year three: honesty above all else.
Next: Is it a mistake to give more than your fair share?