Relationship advice - am I just insecure

Hi! So I’ve been in a relationship for about 4 months now and it’s amazing.

The thing is my whole life I’ve never been treated as attractive, guys would always ask who my friend is etc. And I never really had a bf.

Come to my current partner, I suppose he fancied me because he thought I was very mysterious, this is because I thought he would never like me so kept myself hidden to not get my hopes up, which ended up attracting him.

The problem is, he’s a model. He’s currently with Burberry as I’m writing this and just returned from Paris fashion week. He’s also extremely sexually active, or was, and these are the main reasons why I just don’t think this will last.

Considering the fact that I believe he fancied me for my mystery, as soon as that element of mystery goes, why would he stay with me when he literally is with supermodels all day for a living.

But anyway, does anyone have any contributions as to whether I’m right in my assumptions or if I’m just going crazy! Thank you.