Hum. I definitely feel that way as well. I've got a metric crap tonne of body image issues, but... when it comes right down to it, I have to remind myself that my boy has seen me (at higher weights, too!), he knows what I look like, and he loves me one way or the other.
So maybe he sees your stretch marks. So what? You look like a completely gorgeous lady, and I can't see him deciding he's no longer attracted to you because of a slight skin discolouration... which will fade more and more as time goes on anyhow...!
Don't read this if you're oversensitive to TMI:
My best parallel rationale ever was an ex boyfriend of mine who absolutely REFUSED to change in the same room as me if there was a chance that I would see *ahem* HIM... er.... unexcited.
And all I could think was how absolutely SILLY he was being! People are self-conscious about all sorts of things, and usually their partners have no idea WHY they're self-conscious over it!
And as we're on the topic.... The first 30 seconds here have always made me quite happy:
http://www.youtube.com/watch?v=c15ohjNzYUM
"I happen to have a very high regard for your wobbly bits.

"
Awwwwwww.