How Can People Be So Terrible?

So there's this guy called Will, he's always been a bit of an idiot.
But he did the most awful thing anybody could ever do to me.

I've been in love with him for nearly a year.
After 10 months of telling him that, and getting knocked back, he asked me out.
We went out for 2 months.
Then four days ago we broke up.
I broke up with him.

We kept arguing, and he wanted a break.
In my opinion breaks never work.
So I broke up with him.

For the next three days we were telling each other we still loved each other.
But we both knew we couldn't get back together.
Though I had considered it so many times.

Then yesterday, he got a new girlfriend. Hannah.

Now let me tell you something about Hannah, she is a whore.
She's the most annoying person in the world but as soon as a guy is around
she turns into this perfect little whore.
I hate her.
When me and Will were going out, I told him if he ever went out with her I'd kill myself.
That it is the worst thing he could ever do to me.
He'd always say she was ugly, that he never liked her.
And now he's going out with her.

He's still telling people he loves me and doesn't know how he feels about her.
So he must be just using her.

I don't understand how someone could be so cruel.
I've never felt so hurt or betrayed in my life.

I'm in love with him!
and he did this.

I'm so confused.