he then smirked and said 'well you do realise no one will ever want you, two kids, stretch marks, socially anxious and Moody
Two kids. No biggie at all. People have children. That's life. If you're at the age where you have children (assuming you weren't a mid-teen mum), then chances are that men your age will have children too. Or at least not be surprised if a woman does have children.
Stretch marks... You've have children. Loads of people (including men) have stretch marks. Very, very few people care. Truly. They really don't matter a jot.
Socially anxious - You can work on that. Probably part of the problem might be anxiety generally. And I'm sure life with your man child ex-h exacerbated that.
Moody - again, no bloody wonder, living with him.
He saw he upset me, gave me a hug and said I'm sorry that all slipped out but its the truth plus you nag too much.
You nagged because you were with him, in a shit relationship, with a man child. When you meet someone who is an functioning independent adult, who doesn't need to be "nagged" to fulfill the minimum obligations of life or expect you to do it all for him, you won't nag. You'll be a happy, carefree joy to be around 
Anyone would be moody and a nag if they are in a crap relationship where one party is not pulling their weight. Because then you have to do the work of two people, and it makes you tired and very resentful.