I would obviously elaborate if I became a bit closer to somebody, I wouldn't carry a lie on.
I'd be surprised if you got the chance with a lot of people. You'd already have lied to them. I'd expect most people would then distance themselves, as you'd have undermined anything else you've told them, and they'd be subliminally wondering what else wasn't quite true.
Maybe just after putting eighteen years into something i want to be able to have some reference to it. I want my children to have that too.
I suspect that is the crux and you need to do some mindset work about it. You do have something for it. You have 18 years of a relationship and children. You don't have a marriage, because there wasn't one. You can tell people you were engaged when you reach that point with them, if you want to, but it's not unusual for people not to marry these days - and if it was some kind of status being married, being divorced would surely lose it anyway?
Your children have two parents, they don't need them to have been married, and you weren't.
At any point that you refer to being divorced, you could instead just refer to your previous long-term relationship... but generally, whether it's on dating profiles or in social situations, you're better focusing on you and your current situation and not your marital status.
You're just fine as you are. Your children are fine. Your long-term relationship is fine. It's not unusual to have been in a long relationship and not married... but it would be unusual to lie about it.