Paranoid and need advice....("._.)

So I started dating one of my friends, who's freaking adorable and one of the coolest and most loving guys ever, but....I can't shake the worry of heartbreak out of my head. I've never dater anyone anymore, versus him, who's had two relationships before me (one of who I actually know and am kind of acquaintances with) so this is basically my life now:

omg, what if he doesn't like this?

Why didn't I notice that?

What if he thinks I'm a bad girlfriend?

WHAT IF I AM A BAD GIRLFRIEND?!

He secretly hates you.

Let's worry about his ex killing you forever now.

He's gonna break up with you.

You weren't prepared for this.

My emotions are going every which way.

Should you kiss him....no...yes?

I regret not kissing him, gosh dangit!

He's so upfront about this kinda stuff....Maybe you should say what you feel too...no, he'll think you're weird.

What if he cheats on me...oh, com'on! he wouldn't do that.....OR WOULD HE?

And many, MANY more thoughts that roll through my head every time I think about him....;-;

If any, more experienced girlies are reading...how do you stop worrying about little things? How do you just let yourself be happy, because I have never been more insecure in my life.

Thanks for existing!