Isa,

If you  allow someone else to determine how you yourself feel about yourself, then you've given them all the power there is.  Don't do that.  Okay, so maybe this job hasnt turned out to be the best of the best for you.  Are you a professional? Are you good at what you do? Did you think so before this one person offered his opinion? Of course you did! you were out there in the job market selling yourself to prospective employers.  The reason you're being hit so hard by this negative turn is that you thought you had found a home, a professional home at least.  Where you'd be safe from the horrors and stress of job hunting.  Let's face it no one likes that.

Now you find out that you've got no "home" in fact you're on a leaky boat which is taking on water fast.  Some of that water you're adding yourself because you no longer believe you can get that boat to go anywhere.

The shore's in sight kiddo, are you going to sit there and wait while the boat fills up with water or will you swim for it? Or maybe even bail a little.

Before you give up on yourself, a little communication with the employer is in order.  But you're so down on yourself I hestitate to suggest it.  Communication only really works when you're coming from a powerful place inside, otherwise the tendancy is to place blame.  When you're feeling bad and someone brings up something you've done it's the path of least resistance to find a way to blame someone else rather than listen to what the other guy is saying and try to fathom if the problem is something you can correct.

You know, when you're baking a cake, you've got a certain amount of leeway with the flour. A bit too much the thing might be dry, but it will still pretty much look and act like a cake.  Too little though and it never turns into anything useful.  It doesn't rise, it just sits there in the pan, and you wonder what it could have been.

communication is like that.  And Sweetie even if you're the world's WORST office professional, which I seriously doubt, you can add a bit more flour and still end up with a cake. It's when you don't try that you don't get, and right now you need to be trying to explain to yourself, that you are not all things to all people and sometimes people don't mesh well and sometimes people say things and have no real idea of their impact on another person.

Ask yourself this:
You're still in your first 90 days of employment.  Your employer could have easily said  "Uhhh this is not working for me, let's part friends have a nice life"

Rather than being miserable, why not consider some positives here?

Your employer decided to extend your probationary status
Your employer gave you some things to work on, even if, in your opinion they were not all correct, at least he's given you something to start with.

Why not consider creating a plan to address some of his issues in a way that you think makes sense, and *gasp* ask his input? I bet if you can make yourself do it, you might see an attitude change in him.  

Tell him you were distressed by the review, don't cry and don't blame, tell him you'd like to bring your work up to his standards and then ASK him for his advice on how to do just that.

Now, you've got your power back because once you ask him and he offers some advice, it's totally your decision as to whether you'd like to follow that advice or not.

Go on, bake a cake, what have you really got to lose?

Andrea