ADVICE!! HIS EX....

So basically I've started talking to/ dating this guy and I like him A LOT, but

His last gf he dated for a few years and she's so gorgeous- so pretty

And I feel so inferior to her every since we started talking I've felt nothing but ugly and I don't know why, he's never said anything rude about my appearance.

Maybe I fear them getting back together or him choosing her or something like that.

I've never been in a relationship like this before and I need advice. I've never had to "worry" about an ex. It's killing me for no reason I know it's wrong to feel this way but I didn't not know how not to. That's where I need help