My husband hates when I ask him clothing questions. Dreads it.
This topic is often in stand up comedy routines for this very reason.
This is what girlfriends are for. Good girlfriends know how to be honest, but they are kind :)
It's kind of the same with asking men about our bodies. You just don't go there.
Has your boyfriend/partner learned this? Ah sadly no.
I can't tell if he is a jerk or just saying what he's thinking, no filter - or both. He hasn't learned the golden rule - you don't compare women to other women, and you don't compare us to what we were before. You certainly don't voice it.
The thing is, men's bodies change too - and it would be like us saying "Hey, remember when you were smokin' hot before you had that belly?". We don't, and the thing is, they don't ask.
He was a jerk for saying it for sure. However, I'm sure he thinks you are smokin' hot. Men really don't care about this stuff - stretch marks, cellulite, etc. I am tiny and have cellulite. My husband doesn't even get it is cellulite. He has asked "Where?". They honestly like the overall form of a woman. That's what does the 'Schwing' (Wayne's World) thing for them. They do not notice every little flaw we have.
Is your guy a jerk otherwise? If so, bigger issue.
My advice - just know you're gorgeous as you are, no one looks the same after kids or as we age, and that's totally fine - we're still beauties. Remember, those young gals are insecure too. Work on your insecurity. You alone can do that, he can't fix it.
I'd leave him out of it :) Best to you.
* My suggestion would be to say you weren't asking him to compare your physique to his nephew's girlfriend's. You were asking about the weather. I can't say my husband ever said something like your partner said to you - no. He said other bumbling things though - but nothing as inconsiderate or as rude. My husband's more a twit but has learned. He means well and thinks he's lucky to be with me. If your guy doesn't feel that way, I think we're all saying, there's bigger issues. But focus on your own self worth. He can't give you that.